
THE 26-INCH EQUATORIAL OF THE UNITED STATES NAVAL 

OBSERVATORY WITH WHICH THE SATELLITES OF MARS WERE 

DISCOVERED IN 1 877 



Splendors of the Sky 



BY 



ISABEL MARTIN LEWIS, A.M. 

(Connected with the Nautical Almanac Office 
of the U. S. Naval Observatory) 




NEW YORK 

DUFFIELD & COMPANY 

1919 



Q3H 
3JT 



Copyright, 1919, by 
DUFFIELD & COMPANY 



OCI lb 1919 



)CI.A536 



18 , > x - 



/v\ O 



CONTENTS 



CHAPTER 

I. 

II. 

III. 

IV. 

V. 

VI. 

VII. 

VIII. 

IX. 

X. 

XI. 

XII. 

XIII. 

XIV. 

XV. 

XVI. 

XVII. 

XVIII. 

XIX. 

XX. 

XXI. 

XXII. 

XXIII. 

XXIV. 



PAGE 

Vassals of the Sun i 

The Origin of the Solar System . 10 

Evasive Mercury 17 

Venus, Earth's Sister Planet . . 24 

How Old Is Mother Earth? ... 31 

Mysteries of Mars ...... 39 

The Asteroids 46 

The Planets Jupiter and Saturn Com- 
pared 53 

Saturn the Ringed Planet .... 61 

Plain Facts About the Moon ... 66 

Some Unsolved Problems of the Moon 74 

Shooting Stars and Meteors ... 82 

Our Celestial Visitors, Comets . . 91 
How Carbon Dioxide in the Earth's 

Atmosphere Affects Climate . . 98 
How a Little Spectroscope Tells the 

Secret of Light 106 

Secrets of the Sun Revealed by the 

Spectroscope ........ 115 

The Spots on the Sun 124 

Solar Explosions ....... 132 

Some Recent Eclipses — Their Value 

to Astronomy 140 

Are There Other Planet Worlds? . 157 

Drift of the Star Streams .... 165 

The Milky Way 172 

Do Dark Stars Exist in the Heavens? 179 
The Brilliant Nova of 1918, Nova 

Aquil^ No. 3 ........ 186 



CONTENTS 



CHAPTER PAGE 

XXV. Calcium Gas in the Milky Way . . 193 
XXVI. The Spiral Nebulae and the Great 

Nebula in Andromeda 200 

XXVII. Gaseous Nebulae and the Origin of the 

Stars 208 

XXVIII. The Gleat Star Cluster in Hercules 216 
XXIX. Wonders of the Globular Star Clus- 
ters 223 

XXX. The Life of a Star 232 

XXXI. Stellar Evolution and the "Missing 

Link" Star 240 

XXXII. Dwarf Star Hotter Than the Sun . 248 

XXXIII. Photography of the Heavens . . . 255 

XXXIV. The Photographic Plate — the Astron- 

omer's Eye 263 

XXXV. The Story of a Runaway Star . . 270 

XXXVI. Measuring Star Distances .... 276 

XXXVII. Laying Stars in the Balances . . 286 

XXXVIII. Wonders of Orion 295 

XXXIX. The Constellations of Winter . . . 301 

XL. The Constellations of Spring . . . 310 

XLI. The Constellations of Summer . . 316 

XLII. The Constellations of Autumn . . 322 

XLIII. Brilliant Stars of the Southern 

Hemisphere 329 

XLIV. The One-Hundred Inch Telescope of 

Mount Wilson Observatory . . . 336 



LIST OF ILLUSTRATIONS 

PAGE 

The 26-Inch Equatorial of the United States 
Naval Observatory with Which the Satellites 
of Mars Were Discovered in 1877 . . Frontispiece 

Solar Prominence 140,000 Miles High . ... ... 28 

The Moon — Age, 8^2 Days .. . . . . > > : . 70 

Brooks' Comet ......... y . > . . 94 

The Great Nebula in Orion .... . . .. . 126 

Dark Markings in the Milky Way ...... 174 

The Great Spiral Nebula in Andromeda .... 202 

The Corona of the Total Solar Eclipse of May 

17, 1901 . . .... . . ... . 260 



PREFACE 

The following book has been compiled from a 
series of articles written by the author during the 
past three years for " The New York Evening Sun" 
upon astronomical subjects of general, popular 
interests. 

Requests from a number of readers for copies of 
these articles have led to the publication of a 
selection and arrangement of them, including some 
revisions and changes, which form a connected and 
comprehensive treatment of the astronomy of the 
present day. 

Diagrams, formulae and mathematical proofs 
have been entirely omitted as unsuitable to a 
popular treatment of the subject. It is not the 
desire of the author to attempt to enter into a 
detailed scientific exposition of astronomical truths 
but simply to tell in non-technical terms something 
about the wonderful progress the astronomers are 
now making in delving into the mysteries of time 
and space and in solving problems concerning the 
heavenly bodies that a few years ago appeared to be 
beyond solution. 



CHAPTER I 



VASSALS OF THE SUN 



TTTHO has not admired the brilliant and beau- 
™ * tiful planets, members of our own solar 
system — glorious Venus, fiery Mars, ringed Saturn 
and magnificent Jupiter ? Possibly some of us have 
also spied in the twilight hour following sunset 
or preceding sunrise elusive Mercury, closest at- 
tendant of the sun. 

From remotest antiquity these five planets have 
been observed apparently wandering among the 
fixed stars, though in truth separated from them 
by inconceivable immensities of space. Eight plan- 
ets in all, including our own little planet earth, 
with their attendant moons, unceasingly encircle 
the sun in obedience to the universal and myste- 
rious law of gravitation. To modern astronomers 
we owe the discovery of the two outermost planets, 

1 



SPLENDORS OF THE SKY 

Uranus, just at the limit of visibility of the un- 
aided eye, and Neptune, barely showing in small 
telescopes the planetary disk that distinguishes it 
from the fixed stars far beyond. 

Of the nearer planets, Mercury is by far the 
most difficult to observe, for it is lost in the solar 
rays most of the time. In less than three months, 
eighty-eight days to be exact, Mercury completes 
one trip around the sun. During a considerable 
portion of this time the planet is either hidden be- 
hind the sun or passing between us and the sun. 
It is only when farthest to the east or west of the 
sun, at elongations, that it is observable. As Mer- 
cury can never depart more than twenty-eight de- 
grees from the sun, even under the most favorable 
circumstances, it usually escapes detection. At 
eastern elongations Mercury sets after the sun and 
is evening star. At western elongations it may be 
seen in the twilight hours just preceding sunrise as 
morning star, and when found delights us by ap- 
pearing as a beautiful star about as bright as bril- 
liant Vega. Mercury is the nearest to the sun of all 
the planets, also the smallest, the hottest and the 
fleetest. Its orbit departs more from the circular 
shape than does the orbit of any other planet, so that 

2 



SPLENDORS OF THE SKY 



the planet's distance from the sun varies as much 
as fifteen million miles. The diameter of Mercury 
is only three thousand miles and both Jupiter and 
Saturn have satellites that surpass Mercury in size. 
It is almost a certainty that Mercury always turns 
the same face toward the sun. The temperature, 
therefore, is torrid on one side, frigid on the other, 
and the temperature differences are made all the 
more extreme from the fact that Mercury has no 
atmosphere, probably, as is the case with the moon, 
because it has not sufficient gravitational force to 
hold one. 

In Venus we behold our sister planet. The 
diameter of this planet is about two hundred miles 
less than that of our own planet. Venus far sur- 
passes all the other planets in brilliancy, even Jupi- 
ter, the giant among them all, cannot rival her in 
splendor. This is due to the fact that she is nearer 
to us than any other planet, at nearest approach 
only 26,000,000 miles away. In strong contrast 
to Mercury, Venus is surrounded by a dense atmos- 
phere. The surface of the planet is hidden by 
clouds and no surface markings can be distin- 
guished with certainty, and so it is still undecided 
whether Venus rotates on its axis in a day about 

3 



SPLENDORS OF THE SKY 



equal in length, to our own day or turns the same 
face toward the sun. Most astronomers now in- 
cline to the belief that the same face is always 
toward the sun. Even were the latter the true 
condition, Venus would not have the extremes of 
temperature found upon Mercury, partly because 
its distance from the sun is much greater and 
partly because of its dense atmosphere. Winds of 
such intensity as we never experience upon the 
earth would constantly pass between the hot and 
cold sides of the planet, tending to equalize the 
great extremes of temperature existing upon the 
two sides. 

Mercury and Venus, as far as we know, are un- 
attended by satellites and are the only two planets 
in the solar system of which this is true. Since 
they have orbits lying between the earth and the 
sun they also have phases similar to those of the 
moon. Venus never can be seen more than forty- 
seven degrees from the sun and so is either morn- 
ing or evening star. She can never be seen 
overhead in the evening, but always appears in the 
eastern or western skies, in early morning hours 
in the east, preceding sunrise, or in early evening 
hours in the west, following sunset. 



SPLENDORS OF THE SKY 



Mars, the small world that has aroused so much 
controversy because of its peculiar surface mark- 
ings, lies next beyond the earth as we pass out- 
ward from the sun. Its diameter is somewhat more 
than half and its surface area less than one-third 
that of the earth. Its green and reddish patches, 
its snow caps and its much-talked-of " canals" have 
interested even those most indifferent to the mys- 
teries of the heavens. Mars is the last of the ter- 
restrial or inner group of planets, Mercury, Venus, 
Earth and Mars, as distinguished from the major 
planets, Jupiter, Saturn, Uranus and Neptune. 

The orbit of Mars, which is 142,000,000 miles 
from the sun, is separated from the orbit of Jupi- 
ter by a vast expanse of 350,000,000 miles. 
In this immense zone are found the orbits of the 
asteroids or planetoids, mere fragments of planet- 
ary matter that in no case possess a diameter 
greater than 500 miles. To find names for the 
members of this numerous group and keep track 
of their movements is becoming a burdensome task 
for the astronomer. They are now numbered by 
hundreds. It was once believed they were frag- 
ments of a shattered planet, but it is now thought 
they are rather the material for a planet that was 

5 



SPLENDORS OF THE SKY 



never allowed to take form, due to the disruptive 
effect of Jupiter's mighty mass. 

The major planets are distinguished from the 
terrestrial group by their great size, enormous dis- 
tances from the sun and extremely low density, 
not much exceeding that of water — in the case of 
Saturn even less. The density of the terrestrial 
group is extremely high. Our own planet, which 
possesses the highest density of all the planets, has 
5.5 times the density of water. 

This low density of the outer planets implies 
they are still mostly in a gaseous condition. 

Jupiter, the largest of the planets, has a mass 
two and one half times as great as all the other 
planets combined. He is also the centre of a large 
satellite system of nine moons, two of which 
surpass the planet Mercury in size. Four of these 
moons have been known from the days of Galileo 
and can be observed even with an opera glass. 

Saturn, next beyond Jupiter, is noted for its 
wonderful system of concentric rings, composed of 
countless tiny moonlets, and its large satellite fam- 
ily of nine moons. Titan, the largest, has a diam- 
eter of 3,500 miles, which places it between Mer- 
cury and Mars in size. Saturn is also remarkable 

6 



SPLENDORS OF THE SKY 



for the fact that its density is less than water. It 
is the only planet in the solar systems that would 
float in water. 

It is almost impossible for the human mind to 
grasp the immensity of this solar system of ours 
and realize as well that even the solar system is 
but one of millions of systems that form the stellar 
universe. 

If we should try to represent our solar system to 
scale and should choose for the sun a globe two and 
a half feet in diameter, Jupiter would be a ball 
three inches in diameter. Saturn would be a little 
over two and a half inches in diameter, Uranus and 
Neptune balls of nearly equal size, a little more 
than one inch in diameter, Uranus exceeding Nep- 
Imne in diameter by about one-tenth of an inch, 
while the terrestrial group would appear insignifi- 
cant beside these larger members of our system. 
Venus and our own Earth on this scale would be 
but one-quarter of an inch in diameter, while Mars 
and Mercury would have diameters one-seventh and 
one-tenth of an inch respectively. Placed at the 
distance of the nearest star our largest telescopes 
would fail to reveal the existence of Jupiter, the 
largest of all the planets. 

7 



SPLENDORS OF THE SKY 



To form some idea of the relative distances of 
the planets from the sun, let lis consider the time 
that it takes a ray of sunlight to reach each of the 
planetary orbits travelling outward from the sun 
at a speed of 186,000 miles per second. Three min- 
utes after leaving the sun it crosses the orbit of 
Mercury, at the end of six minutes it passes the 
orbit of Venus, eight and a fraction minutes it 
requires to reach the earth's orbit, and nearly 
thirteen minutes after leaving the sun it arrives at 
the orbit of Mars. Darting into the vast abyss 
lying beyond Mars' orbit, it travels fully thirty 
minutes longer before it comes to the orbit of Jupi- 
ter. Thirty-six more minutes pass before it comes 
to Saturn's orbit. It takes more than two and a 
half hours for this ray of sunlight to travel from 
the sun to the orbit of Uranus. More than four 
hours after the time it started it finally comes to 
the orbit of Neptune at a distance of nearly 2,800,- 
000,000 miles from the sun. From here it speeds 
onward to the stars beyond and reaches the nearest 
in four and a half years. 

The periods of revolution of the planets around 
the sun differ as widely as their masses and dis- 
tances from the sun. In eighty-eight days Mer- 

8 



SPLENDORS OF THE SKY 



cury completes its rapid journey. Venus requires 
seven and one-half months, Mars six hundred and 
eighty-seven days. Twelve years pass by, however, 
before Jupiter makes one trip around the sun. Sat- 
urn requires twenty-nine and one-half years, Ur- 
anus eighty-four years, and nearly one hundred and 
sixty-five years elapse before Neptune sweeps en- 
tirely around his mighty path through the heavens. 



9 



CHAPTER II 

THE ORIGIN OF THE SOLAR SYSTEM 

*Tp HAT the material of which the sun and plan- 
-*■ ets are fashioned originally existed in the 
form of a nebulous mass practically all astrono- 
mers believe; but the process by which our solar 
system developed from a chaotic nebula into an 
orderly and well-regulated family of planets re- 
volving around a central sun is one of the fascinat- 
ing and puzzling problems of astronomy. 

Near the end of the eighteenth century the fam- 
ous mathematician and astronomer La Place, ad- 
vanced his noted nebular hypothesis of the origin 
of the solar system which gained universal ac- 
ceptance almost immediately and held undisputed 
sway for nearly an entire century. Modifications 
and changes had to be made at times, however, to 
adapt the theory to later discoveries, and finally in 
10 



SPLENDORS OF THE SKY 



the light of more recent researches an almost com- 
plete abandonment of the theory has resulted. 

According to the nebular hypothesis, a vast gas- 
eous nebula originally extended beyond the present 
orbit of the outermost planet, Neptune, and slowly 
rotated in the direction in which the planets now 
revolve around the sun. Such a great mass would 
lose heat by radiation into space and would con- 
tract. As the rotating mass contracted it would 
of necessity rotate faster and faster, and as a re- 
sult equatorial rings of nebulous matter would be 
abandoned, which would have a tendency to break 
unless perfectly uniform and circular. Excess of 
material at any one point in the ring would draw 
to itself the remaining material in the ring. The 
result would be the formation of a planet which 
would continue to revolve around the central con- 
tracting nebula at the distance at which the ring 
was abandoned. Other rings left behind at vari- 
ous stages as the central nebulous mass continued 
to contract, would form additional planets. The 
globular masses formed when the abandoned rings 
broke up might, in the same manner, contract and 
leave behind rings which would go to form the 
satellites by which most of the planets are at- 

IX 



SPLENDORS OF THE SKY 



tended. The rings of Saturn were supposed to be 
rings abandoned by the contracting mass of that 
planet, which, for some reason, had kept their orig- 
inal form. The earth, according to the nebular 
hypothesis, was once in a gaseous condition and 
gradually cooled down to its present form of sur- 
face crust and molten interior. The theory of La 
Place was in accord with all the facts then known 
concerning the solar system. It seemed to explain 
satisfactorily why the planets move in orbits that 
are almost perfect circles and why they all turn 
on their axes and revolve around the sun in the 
same direction, namely from west to east, and also 
why they all revolve around the sun in nearly the 
same plane. 

The asteroids or planetoids, however, furnish 
notable exceptions to these laws. At the time La 
Place advanced his theory they had not been dis- 
covered. These small members of our systems are 
now numbered by hundreds. The diameter of the 
largest does not exceed five hundred miles, and 
most of them are much smaller. Their orbits lie 
between the orbits of Mars and Jupiter and are 
remarkably different from the orbits of the major 
planets, for they vary in shape from almost per- 
12 



SPLENDORS OF THE SKY 



feet circles to ellipses as elongated as some comet- 
ary orbits. Instead of lying in nearly the 
same plane as is the case with the major planets, 
they intersect the common plane at all angles from 
zero to thirty-five degrees, and could, therefore, 
never have been formed from an abandoned ring 
of the contracting solar nebula. 

Moreover, it has been discovered that certain 
satellites of the outer planets do not share the com- 
mon direction of revolution of the planets from 
west to east, but move in a retrograde motion 
around their primaries from east to west. Also, 
according to the nebular hypothesis, no satellite 
could revolve around its primary in less time than 
its primary takes to turn on its axis; but Phobos, 
the inner satellite of Mars, finishes three revolu- 
tions and starts on a fourth before Mars has turned 
once on its axis. The moonlets composing the inner 
ring of Saturn also complete circuits in between 
five and six hours, although Saturn requires ten 
and a half hours to rotate on its axis. Other in- 
stances might be cited to show the failure of the 
nebular hypothesis to explain all the facts now 
known concerning our solar system. This noted 
hypothesis served as a good working hypothesis in 

13 



SPLENDORS OF THE SKY 



its day, nevertheless, and greatly stimulated inves- 
tigations in the allied sciences of geology, zoology 
and biology in the nineteenth century. It is far 
easier to tear down a theory than to build up a new 
one that will fit in with all the observed facts. Sev- 
eral new theories of the origin of the solar system 
have been advanced, but no one theory seems satis- 
factory in all respects. Astronomical discoveries 
of recent years have shown our solar system to be a 
more complicated mechanism than was at first sus- 
pected. 

The idea that the nebula from which the solar 
system was evolved was originally spiral in form 
is now quite generally held. Chamberlin and 
Moulton have developed a theory of the origin of 
the solar system along these lines, known as the 
Planetesimal Theory. It can be shown that a spiral 
nebula might arise through the close approach of 
two stars, or from the approach of two nebulous 
streams and their curling together by mutual at- 
traction, or by the curling up of a single nebulous 
stream, due to its own gravitation. There are 
probably close to two billion luminous stars in our 
stellar system, all in motion, and we can reasonably 
assume that collisions or close approaches will oc- 
14 



SPLENDORS OF THE SKY 



cur despite the fact that enormous distances sepa- 
rate the stars from one another. When we admit, 
as actual discovery forces us to, the existence of 
dark stars and dark star systems and dark nebu- 
lous matter, as well as bright, the likelihood of oc- 
casional collisions or close approaches increases. It 
has also been found that the nebula from which a 
solar system evolves need not necessarily be gas- 
eous or at high temperature, since a nebulous 
swarm of meteoric particles would act in the same} 
way as the molecules of gas in a gaseous nebula. 

In favor of the belief that the original solar neb- 
ula was spiral in form, it can be shown that, while 
no nebula of the form required by the nebular hy- 
pothesis of La Place is known to exist, the spiral 
form of nebula aoounds throughout the universe. 
Even the stellar universe itself may consist of stars 
streaming in obedience to the laws governing a 
spiral formation. Although we are still uncertain 
as to the exact manner of the evolution of 
our solar system from the primitive nebula, proofs 
of the fact that suns evolve from nebulae and pass 
through all the stages from youth to old age are 
written in the heavens themselves. A careful sur- 
vey of the heavens shows stars not yet freed of 

15 



SPLENDORS OF THE SKY 



their nebulous appendages, and even whole clusters 
of stars wrapped in nebulous matter. All stages 
of evolution are represented from the blue stars of 
youth to the feebly flickering red stars of old age 
and the cold, dark stars that have lived their lives 
and speed onward through space until the time 
comes, when they may start perchance, upon a new 
life, through some celestial catastrophe. 



16 



CHAPTER III 



EVASIVE MERCURY 



T% yTERCURY is the most difficult to observe of 
-*-▼ A a n the satellites of the sun, because it never 
departs more than twenty-eight degrees from its 
ruler, even under the most favorable circumstances, 
and is usually entirely concealed by the blinding 
rays of the sun. 

Spring is the best time to view this planet as 
evening star, and autumn the most favorable time 
to search for it as morning star, since the ecliptic, 
the path of the sun, near which the moon and the 
planets are always to be found, then rises most 
sharply along the horizon. 

Mercury can only be seen for about two weeks at 
a time near the dates of its elongations. The planet 
is, of course, found with great difficulty in high 
latitudes and is rarely seen in northern Europe. 

17 



SPLENDORS OF THE SKY 

In fact, comparatively few people have ever seen 
this closest attendant of the sun. Copernicus, so 
we are told, never saw it. 

When seen at time of elongation, near the hori- 
zon, Mercury usually has a slightly reddish tinge, 
due to the fact that its rays are travelling through 
the denser lower strata of the atmosphere. It will 
also appear to twinkle somewhat for the same rea- 
son. Mercury is, in fact, sometimes referred to as 
"the twinkler." 

All the other planets shine with calm, steady 
light, and it is interesting to compare Mercury, if 
it can be found, with the other bright planets when 
they are visible at the same time. 

Most astronomical observations of Mercury are 
made in full daylight by screening off the light of 
the sun. Sunlight is less disturbing to observations 
made with large telescopes than the dense haze of 
sunset and sunrise skies. It is due largely to the 
difficulties of observing this planet that the period 
of its rotation on its axis and, therefore, the length 
of its day and night has not been settled beyond 
question. 

It is virtually certain, though, that the planet's 
rotation period is equal to the period of its revolu- 
18 



SPLENDORS OF THE SKY 



tion around the sun, or eighty-eight days, and that 
it always keeps the same face turned toward the 
sun. If this is the case there are two longitudinal 
zones on the planet's surface forty-seven degrees 
in width that experience a rising and setting of the 
sun and have forty-four days of light, followed by 
an equal period of darkness. This is due to the 
great ellipticity of the planet's orbit, which departs 
more from a circular form than that of any other 
planet in the solar system. 

The planet's rate of rotation on its axis is uni- 
form, but its rate of revolution around the sun, 
due to the high eccentricity of its orbit, varies from 
thirty-six miles a second at perihelion to twenty- 
three miles a second at aphelion. So there are 
times when Mercury falls behind its mean position 
by as much as twenty-three and one-half degrees, 
and times when it darts ahead of its mean position 
by an equal amount. 

As a result the sun's rays fall first twenty-three 
and one-half degrees beyond the point on the plan- 
et's surface where they would fall if the orbit were 
circular, and then twenty-three and one-half de- 
grees short of this position. This gives rise to the 
two zones forty-seven degrees wide and diametric- 

19 



SPLENDORS OF THE SKY 



ally opposite each other that have an alternate day 
and night, each equal in length to forty-four ter- 
restrial days. Between these two lie the two zones, 
each one hundred and thirty-three degrees wide, 
one of perpetual day and the other of perpetual 
night. 

On the daylight side of the planet the sun ap- 
pears to oscillate backward and forward through 
an angle of forty-seven degrees, and the lowest tem- 
perature is higher than that of the boiling point 
of water upon the earth. Upon the night side the 
only light is that furnished by the stars that shine 
with a radiance and glory unknown to us who dwell 
in a world that is always surrounded by a dense, 
obscuring atmosphere. Mercury has no appreci- 
able atmosphere and the terrible cold of space pre- 
vailing upon the night side of the planet is un- 
tempered by warm air currents, such as would flow 
from the hot to the cold side if the planet possessed 
an atmosphere. 

Here exists a world of extremes, scorched 
on one side, frozen on the other, while in 
the zones of alternate day and night that lie 
between is to be found all the range of temper- 
ature that lies between the two extremes. Lack of 
20 



SPLENDORS OF THE SKY 



atmosphere on Mercury prohibits the existence of 
life. 

The planet reflects about fourteen per cent, of 
the sunlight it receives, which is slightly less than 
the amount reflected by the moon's surface and it 
is believed that its surface resembles that of our 
satellite in being barren and mountainous. 

The axis of the planet is probably perpendicular 
to its orbit, and it has, for this reason, no seasons, 
though its greatly varying distance from the sun 
produces the same effect. The average distance of 
the planet from the sun is 36,000,000 miles. At 
perihelion its distance is 7,500,000 miles less than 
this amount and at aphelion 7,500,000 miles greater. 
The heat and light received from the sun while in 
these two positions vary in the ratio of nine to 
four. A marked increase in the apparent size of 
the sun would be noticed in passing from aphelion 
to perihelion and a corresponding decrease in pass- 
ing from perihelion back to aphelion. 

Mercury is not only the smallest of all the plan- 
ets, but it is even surpassed in size by Titan, one 
of the satellites of Saturn and Ganymede, the third 
satellite of Jupiter. 

The fact that the perihelion of Mercury moves 
21 



SPLENDORS OF THE SKY 



faster than it would move if acted upon only by 
known laws has long been a subject for astronomi- 
cal investigation, and many theories have been ad- 
vanced in explanation, among them the theory of 
the existence of an intra-mercurial planet. Ac- 
cording to Leverrier, the noted French mathema- 
tician, the mass of such a planet would need to be 
one-half the mass of Mercury itself in order to ac- 
count for the actual discrepancy existing between 
the observed and computed values. 

It is virtually certain as a result of careful ex- 
amination of many photographs taken at the time 
of total eclipses of the sun that no object exists 
within the orbit of Mercury with a diameter ex- 
ceeding thirty or forty miles. There is the possi- 
bility that a number of minute bodies of asteroidal 
size may revolve around the sun within the orbit 
of Mercury, but it is very improbable that their 
combined mass would total half the mass of Mer- 
cury. 

So we may assume that Mercury enjoys the 
distinction of being the smallest of all the plan- 
ets, and also the nearest to the sun. It is, in fact, 
distinctive in many ways. Its orbit is the most 
elliptical and the most highly inclined to the eclip- 
22 



SPLENDORS OF THE SKY 



tic of all the planetary orbits. The planet itself 
is the most rarely seen of all planets visible to the 
naked eye, and the only one that does not possess 
an atmosphere. 



23 



CHAPTEE IV 

VENUS, EARTH'S SISTER PLANET 

^T^HE silvery radiance of Earth's sister planet, 
•*■ Venus, attracts the attention of all whenever 
she appears in the western sky, since she is then 
the most beautiful and conspicuous stellar object 
in the heavens. Though fully as beautiful when 
she is visible as "morning star" before sunrise, 
few of us are up at that time to admire her. 

Half way between the horizon and the zenith 
marks the limit of her departure from the sun. 
Since the orbit of Venus lies between us and the 
sun we may never see her in opposition to the sun 
or upon the meridian at midnight, as we do the 
outer planets, Mars, Jupiter and Saturn, and, un- 
like these planets, Venus does not show a circular 
disk in the telescope, but exhibits all the phases 
of the moon and when at her greatest brilliancy 
24 



SPLENDORS OF THE SKY 



appears like a crescent moon in the telescope. 
Although Venus approaches nearer the earth 
than any other celestial body except the moon, the 
asteroid Eros, and a chance comet, she is, unfortu- 
nately, entirely invisible at the time of closest ap- 
proach. The phase she then exhibits corresponds 
to that of new moon. Her illuminated face is 
turned toward the sun, her night side toward the 
earth. She is then but 26,000,000 miles away and 
between the earth and sun. Just before and after 
this time, which is spoken of as the time of inferior 
conjunction, she appears as a very thin crescent 
in the telescope, resembling the moon a day or two 
before and after new moon. Near the time of 
nearest approach of the two planets some astrono- 
mers have observed a faint, ashy light upon the 
darkened disk of the planet. As Venus has no sat- 
ellite, this cannot be attributed to reflected moon- 
light, though some have believed it to be due to 
earth shine or the light from our own planet re- 
flected from the surface of Venus. It is extremely 
doubtful that earth shine could be appreciable 
when a distance of fully 26,000,000 miles separates 
the two bodies, though our planet presents to 
Venus at this time the phase of the full moon and 

25 



SPLENDORS OF THE SKY 



appears much larger and more brilliant to Venus 
than Venus ever does to us. That it may be due 
to some electrical manifestation in the planet's at- 
mosphere similar to auroral displays in our own 
seems more reasonable. It is also near the time of 
closest approach that a very faint ring of light may 
be observed outlining the disk of the planet. This 
is caused by the reflected sunlight from the dense 
atmosphere that surrounds the planet and fur- 
nishes one of many proofs of the existence of such 
an atmosphere. 

If higher forms of life exist upon our sister 
planet and dense clouds do not always completely 
hide the heavens, we may imagine with what in- 
terest our own little earth-moon system would be 
observed at this time of closest approach of the two 
bodies. A most beautiful and interesting double 
star our earth-moon system must appear from 
Venus. Our satellite, of course, would be plainly 
visible to the naked eye from Venus and its con- 
stantly varying positions with reference to our 
planet would soon reveal the fact that it is in rev- 
olution around the earth. How intelligent beings 
there might puzzle over the earth's continents and 
seas, changing vegetation, polar snow caps, clouds, 
26 



SPLENDORS OF THE SKY 



daily rotation and sensational changes ! Just as we 
puzzle over Mars and its baffling surface markings 
may not another world be puzzling over our pe- 
culiarities? This may be most unlikely, but it is 
a possibility. About the planet Venus we know 
very little except that its age may be very nearly 
that of our own planet and that it is more suited to 
the development of forms of life such as we have 
upon the earth than any other planet in the sun's 
family, provided it rotates upon its axis once in 
about twenty-four hours. Upon this point we are 
still in doubt, for observations of Venus are always 
made at a disadvantage, owing to the density of its 
atmosphere and the fact that it is always more or 
less unfavorably situated for observation. 

Many markings have been observed upon Venus, 
but, unfortunately, they do not appear the same 
to all observers, and it is still impossible to say 
with certainty whether the actual surface of the 
planet or cloud formations are seen. Even deter- 
minations of the planet's period of rotation by 
means of the spectroscope contradict each other 
flatly. After years of observations we do not yet 
know whether Venus rotates on its axis in twenty- 
four hours or in two hundred and twenty-five days, 

27 



SPLENDORS OF THE SKY, 



the period of its revolution around the sun. In 
the latter case it would always turn the same face 
toward the sun just as our satellite always turns 
the same face toward the earth. If this state of 
affairs exists on Venus one side never sees the sun, 
the other side never sees the heavens studded with 
myriads of stars, but feels the torrid heat of a 
sun immovable in the sky, possibly screened from 
view by friendly clouds. The planet 's dense atmos- 
phere would tend to mitigate the two extremes of 
temperature found on opposite sides of the planet 
by a constant flow of air currents between the two 
sides. In fact, there would be, under such circum- 
stances, storms of frightful intensity continually 
raging over the planet's surface. If, on the other 
hand, Venus turns on its axis in approximately 
twenty-four hours no other planet in the solar sys- 
tem so closely resembles the earth. 

The diameters of the two planets differ by about 
200 miles, and in mass, density and surface gravity 
they are nearly the same. A man weighing 170 
pounds upon the earth would weigh 145 pounds 
upon Venus. We could move about a little more 
easily upon Venus than we do upon our own planet. 
We would probably find the atmosphere very much 
28 




o 

c 

M 

a ~ 
a « 



8 I 

O «j 



SPLENDORS OF THE SKY 



the same. The reflecting power of the atmosphere 
of Venus is very nearly the same as that of the 
thunder heads we often observe in our summer 
skies, which seems to indicate a cloud laden at- 
mosphere for our sister planet. Though some ob- 
servers have placed the density of the atmosphere 
of Venus at twice the density of the earth's at- 
mosphere, others believe they are virtually the 
same. It is in the amount of light and heat re- 
ceived from the sun that we note the greatest 
difference between the two planets. Venus receives 
nearly twice as much light and heat from the sun 
as we do. This may seem to us a rather uncomfort- 
able amount, and we wonder how the inhabitants 
stand it, but possibly they may wonder how we 
exist upon a planet that is so poorly lighted and so 
cold. Upon our own planet we find life flourishing 
under conditions of great diversity. Countless 
forms of life exist under the sea and upon the 
surface of our planet, in the torrid heat of the 
tropics and the frigid cold of the polar regions. 
So life upon Venus does not seem so improbable 
unless it shall be determined eventually that the 
planet always keeps the same face turned toward 
the sun. In case it shall be found that Venus 

29 



SPLENDORS OF THE SKY 



rotates on its axis once in about twenty-f our hours 
we can hardly escape the conclusion that the life 
process must be running its course there as well as 
here. Given all the essentials for the development 
of life, — air and water, heat and light in abund- 
ance, — it seems almost too much to assume that such 
a world is devoid of life. 



30 



CHAPTER V 

HOW OLD IS MOTHER EARTH? 

THE age of Mother Earth is a perplexing ques- 
tion, not only for astronomers but for geol- 
ogists and biologists as well. 

There are many different methods of attacking 
the problem, but all agree that the long series of 
evolutionary changes that have taken place upon 
our planet could not have been brought about in 
any period of time less than tens of millions of 
years. This applies, moreover, simply to the dur- 
ation of the life process upon the earth and does not 
include the ages that must have elapsed from the 
earth's beginning to the time when it was in a con- 
dition suitable for the production of life. 

Geologists and biologists find their evidence of 
the earth's age in the condition of its crust, in the 
stratification of its rocks and the fossil remains of 

31 



SPLENDORS OF THE SKY 



various forms of life formerly existing upon it, 
while for the astronomer the solution of the prob- 
lem is dependent upon how long the sun's light and 
heat have been supplied at the present rate. Bar- 
ring outside interference, such as the close approach 
of a passing sun, the duration of life within the 
solar system depends entirely upon how long the 
sun's supply of radiant energy can be maintained. 

Considering, first, the evidence furnished by the 
biologist for the duration of life upon our planet, 
through examination of fossil remains in rocks of 
different geological formations, it has been found 
that the earliest and most primitive forms of life 
appeared in rocks of earliest formation and a chain 
of increasingly higher and higher forms of life ap- 
peared as the age of the geological formations de- 
creased. In rocks of the latest formation the fossil 
remains of the highest forms of life appeared. 
Noted biologists have placed the period necessary 
for this excessively slow process of evolution as high 
as two billions of years, and though some feel this 
is too high, none can see how such a long chain of 
evolution could have been completed in less than 
some hundreds of millions of years. 

The time required for the disintegration of the 
32 



SPLENDORS OF THE SKY 



original earth material, its deposition on the bot- 
tom of lakes and oceans, stratification and the num- 
berless repetitions of the process that are known 
to have taken place could not be less than one 
hundred millions of years, according to the most 
conservative estimates of geologists. 

Another geological method of determining the 
age of the arth is to compute the time required for 
the oceans to acquire their present salinity. Since 
the rivers carry to the oceans various salts in sol- 
ution and the water evaporated from the oceans 
leaves the minerals behind the salinity of the oceans 
is continually increasing. There is of course some 
divergence of opinions as to how rapidly the salts 
were carried down to the oceans in the earliest 
ages, but no computation makes the time since the 
oceans first started to form less than sixty millions 
of years and some estimates run as high as one 
hundred and forty millions of years. 

The most recent geological method of determin- 
ing the earth's age followed upon the discovery of 
radio-active substances. Uranium degenerates by 
the gradual breaking up of its atoms and radium, 
lead and helium are evolved. 

The relative amounts of these elements in some 
33 



SPLENDORS OF THE SKY 



rocks show how long the process has been going on 
in them. This method appears to give a greater 
age for the earth than that obtained by any other 
method. Those who have made a special study of 
this method have arrived at the conclusion that 
some of these rocks may be two billion years old, 
and that their age at least must be measured by 
hundreds of millions of years. 

For the astronomer the vital question is, How 
long has the sun kept up its present rate of radia- 
tion? Manifestly all life processes upon our earth 
are dependent upon the light and heat furnished 
by our sun. As soon as the supply begins to appre- 
ciably and continually diminish life will begin a 
rapid decline. The ruler of our solar system is 
radiating heat and light into space at an extrava- 
gant rate. The apparent area of the earth as seen 
from the sun is about one-fifteenth the greatest 
apparent area of Venus as seen from the earth. 
From the sun the earth would appear as a small 
point upon the celestial sphere. And yet how 
much heat does our small planet intercept at a 
distance of ninety-three million miles from the 
sun? It has been estimated that the rate at which 
solar energy is intercepted by the whole earth 
H 



SPLENDORS OF THE SKY 



is 230,000,000,000,000 horse-power. The total 
amount of the sun 's radiant energy must therefore 
be inconceivably great, for less than one two- 
billionth of the total amount given forth is inter- 
cepted by the earth. Except for the amount inter- 
cepted by the other planets, placed at ten times 
the amount the earth receives, the boundless supply 
of radiant energy given forth by our sun is wasted, 
according to the ideas of man. It travels onward 
through interstellar space at the rate of 186,000 
miles per second to the stars beyond. 

The theories that the sun's heat is kept up by 
the combustion of the materials of which it is com- 
posed, or that it is simply cooling off without any 
replenishment of its loss of heat, lead to absurd 
results and receive no consideration from astrono- 
mers. In neither ease, under the most favorable 
suppositions, could its present rate of radiation be 
kept up for more than two or three thousand years. 

A theory that is more plausible than either of 
the preceding considers that the sun's heat is main- 
tained by the impact of meteoric matter. Astrono- 
mers have estimated that if a meteor should fall 
into the sun from the distance of the earth its 
velocity would be about 380 miles a second and the 

35 



SPLENDORS OF THE SKY 



heat produced by the impact would be about 23,000 
times the amount produced by the combustion of 
an equal amount of carbon and oxygen. The 
strongest objection to this theory is that it would 
require a much larger total mass of meteors than 
actually exists. Not a sufficient amount of meteor- 
ic matter could possibly exist within the earth's 
orbit for this purpose, and if it came from beyond 
the earth's orbit the earth would also receive suf- 
ficient amounts to materially affect its tempera- 
ture. As a matter of fact the amount of heat that 
the earth actually does receive from meteoric 
matter is negligible. 

The theory that the sun's heat is kept up by its 
own contraction is the only one that at all fits in 
with the requirements, and there are serious ob- 
jections to regarding contraction as the only source 
of supply of the sun's heat. Nevertheless, it can 
be shown, following the methods of Helmholtz and 
using the most recent data for the sun's rate of 
radiation, volume and mass that a contraction of 
120 feet a year in the sun's radius would produce 
as much heat as the sun now radiates annually. 
This amount of contraction is so small that ten 
thousand years would elapse before the resulting 
36 



SPLENDORS OF THE SKY 



change in the apparent diameter of the sun could 
be detected from the distance of the earth with the 
assistance of our most powerful telescopes. So 
whether the sun actually is contracting cannot be 
determined observationally. A weak point of the 
contraction theory is that the present rate of radia- 
tion of the sun could not have been maintained by 
contraction alone for more than twenty-five mill- 
ion years at the most. This would imply that all 
the great series of changes that geologists and 
biologists have every reason to believe extended 
over tens if not hundreds of millions of years were 
crowded into a period of approximately twenty- 
five million years. Most astronomers consider it 
more reasonable to assume that the contraction of 
the sun does not supply all of its heat than to 
assume that all the evidence of other scientists 
collected from a variety of independent sources 
is wrong. 

With the discovery of radioactivity it was be- 
lieved that the sun's supply of heat might be sus- 
tained partly by disintegration of uranium and 
radium, inasmuch as such disintegration is accom- 
panied by the evolution of an enormous amount 
of heat. Although it is not known definitely that 

37 



SPLENDORS OF THE SKY 



these substances are found in the sun, helium, one 
of the products of the disintegration of uranium 
and radium, occurs in great abundance in the sun, 
and, in fact, was first discovered there. Investi- 
gations showed that if one part in eight hundred 
thousand of the sun were radium, heat would be 
produced from this source alone as fast as the sun 
is radiating it at present but that in two thousand 
years hence half the radium would be gone and the 
production of heat would be diminished one-half, 
or that two thousand years ago the amount was 
twice the present amount and the production of 
heat was twice as fast. Since this is not in accord 
with the facts we can conclude that the sun's heat 
is not due to the disintegration of radium to any 
great extent. Uranium yields results just as un- 
satisfactory. ~ 

Of one fact we are certain, t that an unbroken 
chain of life has existed upon our planet for tens 
of millions of years at least and in this period there 
has been no great temperature change and no signs 
of a steady progressive cooling of the sun. Glacial 
epochs and warmer eras have alternated with each 
other, but no sudden or gradual change great 
enough to destroy the chain of life has ever arisen. 
38 



CHAPTER VI 



MYSTERIES OF MARS 



THE ruddy planet Mars, always an object of 
special interest to the inhabitants of our 
planet, Earth, because of its nearness and the still 
unexplained mystery of its surface markings, is best 
studied when it is in opposition to the sun. 

It is then on the meridian at midnight and visible 
throughout the entire night, rising in the east at 
sunset and setting in the west at sunrise. 

At a near opposition, which occurs once in fifteen 
or seventeen years, Mars is a most striking object 
because of its fiery red color. These near opposi- 
tions always occur in August, and the next one 
will take place in 1924, when Mars will be only 
34,000,000 miles from the earth. Mars will also be 
in opposition to the sun in April, 1920, and in 
June, 1922, since oppositions of Mars are separated 

39 



SPLENDORS OF THE SKY 



by intervals of two years and two months. The 
next three oppositions will be particularly favor- 
able for observations of the surface markings of 
this planet. 

Owing to the rarity of the atmosphere of Mars 
it is possible to observe actual surface markings on 
this planet. Mars has no vast oceans such as exist 
upon our own planet. Extensive desert tracts pre- 
dominate and give the planet its characteristic 
reddish color. The comparatively few dark spots 
that are visible lie in the Southern Hemisphere 
and are generally believed to be due to vegetation. 
The atmosphere of the planet is so rare that the 
climate is one of extremes, with a great daily range 
of temperature. The seasons resemble those found 
upon the earth, for the two planets have nearly the 
same inclination to the ecliptic, but the Martian 
year is nearly two of our years in length and the 
Martian seasons last twice as long as our own. The 
planet turns on its axis in a little more than twenty- 
four hours, so the Martian day and night nearly 
equal the terrestrial day and night in length. 

In addition to the extensive, reddish, desert 
patches and the dark patches due to vegetation the 
north and south polar snow caps are distinctive 
40 



SPLENDORS OF THE SKY 

features of the Martian surface, and their appear- 
ance and disappearance with the seasons is well 
known. It is only when we come to a consideration 
of the Martian "canals" that we meet with a diver- 
gence of opinions among astronomers. Though 
there are still astronomers who have never seen the 
canals and astronomers who deny their existence, 
there seems to be fully as many who have observed 
them and are firmly convinced of their actuality. 

The theory of the late Prof. Lowell concerning 
the much disputed canals was that they were chan- 
nels of water bordered by strips of vegetation and 
were built by intelligent beings for the purpose 
of directing the water from the melting polar caps 
through the desert tracts to the opposite hem- 
isphere. According to this theory we see not the 
water channels but the strips of vegetation grow- 
ing upon the banks. More recently Prof. W. H. 
Pickering has advanced a theory concerning the 
nature of the larger and more important canals 
which he speaks of as the "The Theory of Aerial 
Deposition.' ' 

According to this theory the major canals are 
marshes or natural reservoirs fed by storm ladened 
air currents that are constantly passing from re- 

41 



SPLENDORS OF THE SKY 



gions of high, pressure surrounding the melting 
polar cap to the equatorial regions of low pressure. 
The rotation of the planet upon its axis from west 
to east and the resistance of the atmosphere en- 
countered by these air currents in their passage 
toward the equator would give them a curving 
tendency. Therefore the marshes or canals fed by 
these air currents through precipitation of their 
moisture during the chill Martian nights would also 
show the same curvature. By measuring the radius 
of curvature for the more important north polar 
canals Prof. Pickering arrived at a determination 
of the velocity with which the moisture ladened 
air currents blow and he found that the highest ve- 
locity of the wind over any of the southward lead- 
ing canals was about 230 miles per hour. This was 
the velocity found for the northern portions of one 
of the longest canals shortly after the storm had 
started from the polar regions. 

At the southern end of its course the velocity was 
reduced to about nineteen miles per hour. 

Prof. Pickering concluded from an extensive 

study of the curvatures of various canals that it is 

reasonable to assume that the wind in the northern 

hemisphere of Mars does at time reach a velocity of 

42 



SPLENDORS OF THE SKY 

230 miles per hour and that the maximum theo- 
retical velocity cannot be much less than 324 miles 
per hour nor the corresponding pressure of the 
atmosphere less than one-quarter of the pressure 
of the terrestrial atmosphere. This conclusion is 
borne out, he believes, by other considerations such 
as the small force of gravity on Mars, the trans- 
parency of its atmosphere and the lack of perma- 
nent oceans. Upon this assumption the boiling 
point of water upon Mars comes out as 150 degrees 
F. approximately. 

As the north polar cap melts and diminishes in 
size, the amount of moisture carried southward 
by the air currents should also diminish, and there- 
fore the atmospheric pressure and consequently the 
velocity of the wind. As a result the curvature of 
the canals should change slightly and they should 
shift with the season. The greater the velocity of 
the wind the less it will be deflected in its south- 
ward journey. A slight shifting of the polar canals 
has been noted at previous opposition of Mars, and 
it is particularly desired to investigate this ques- 
tion of the shifting of the canals at favorable oppo- 
sitions. 

According to the theory of Prof. Pickering the 
43 



SPLENDORS OF THE SKY 



major Martian canals, those leading from the north 
polar cap southward to the torrid zone, are not 
necessarily the work of intelligent beings, but they 
do serve the purpose of furnishing the northern 
hemisphere with a supply of water in the form of 
natural marshes or reservoirs during the long 
northern summer until the south polar cap starts to 
melt at the coming of the autumnal equinox. Since 
Mars has no great oceans these marshy tracts are 
most essential for the maintenance of vegetable and 
possibly animal life upon the planet. 

In addition to these larger and more important 
canals there are many faint, narrow canals of a 
secondary type. About 500 canals of the faint type 
have been located and named at the Lowell Ob- 
servatory. They are characterized by great uni- 
formity and straightness and by the fact that 
they appear late in the season and in great num- 
bers. 

Prof. Pickering, who is one of the leading ob- 
servers of Mars, considers that the question of their 
origin is still unsettled. It is unknown whether 
they are artificial or an illusion, or mark the path 
of occasional local storms. As to the visibility of 
the canals of Mars, this depends, according to Prof. 
44 



SPLENDORS OF THE SKY 



Pickering, largely upon the conditions of our own 
atmosphere. Under excellent " seeing " conditions, 
it is possible, he believes, to see all of the more 
prominent canals with a four-inch telescope. 



45 



CHAPTER VII 



THE ASTEROIDS 



TN the vast expanse of space that separates the 
■*■ orbit of the outermost member of the terrestrial 
group of planets, Mars, from the nearest and larg- 
est of the major planets, Jupiter, is found that 
numerous host of tiny bodies known as the planet- 
oids or asteroids. 

Lawful members of the solar system they must 
be considered, although they are distinguished from 
the eight large planets not only by their extreme 
minuteness, which renders the largest of them in- 
visible without telescopic aid, but also by a greater 
range in the shape of their orbits and in the in- 
clination of these orbits to the earth's path around 
the sun. The paths of the eight principal planets 
can hardly be distinguished from perfect circles 
and they lie very nearly in the same plane. The 
46 



SPLENDORS OF THE SKY 



asteroids move in paths that vary from almost per- 
fect circles to highly elongated ellipses and these 
paths are sometimes inclined at an angle of nearly 
35 degrees to the planetary orbits, though the 
average is much less. It is truly remarkable, how- 
ever, that all of the asteroids so far discovered, 
more than eight hundred in number, move in the 
same direction around the sun as do the eight chief 
members of the solar system, from west to east. 
This cannot be the result of chance but points to a 
common origin with the other members of the 
system. According to the planetesimal theory of 
the origin of our solar system the asteroids may be 
regarded as particles of the original nebula that es- 
caped fusion into one greater planetary mass, due 
either to an absence of a planetary nucleus in their 
immediate neighborhood or to the nearness of the 
huge Jovian mass under whose disruptive influences 
they have been kept apart. So interwoven are the 
paths of the planetoids that if they were made of 
wire not one could be lifted without drawing the 
others with it. That they have so far escaped col- 
lisions is due to the fact that their paths lie in 
planes inclined at different angles. The noted little 
asteroid Eros has escaped collision with the planet 

47 



SPLENDORS OF THE SKY 



Mars only because of the inclination of its orbit. 
At the time of the discovery of the first asteroid, 
January 1, 1801, the first day of the nineteenth 
century, astronomers were making preparations to 
search for a planet in the enormous gap existing 
between the orbits of Mars and Jupiter. Accord- 
ing to Bode's law, to which is also due, indirectly, 
the discovery of the planet Neptune, a planet was 
to be looked for at about 2.8 times the earth's dis- 
tance from the sun. This peculiar law, which has 
no scientific foundation, gives a rough approxima- 
tion to the relative distances of the first seven 
planets from the sun, as well as the average posi- 
tion of the asteroids. According to this relation- 
ship noted by Bode, if the number 4 is added to 
each number in the series 0, 3, 6, 12, 24, 48, 96, the 
resulting series, 4, 7, 10, 16, 28, 52, 100, repre- 
resents roughly the relative distances of the planets 
Mercury, Venus, Earth, Mars, Jupiter and Saturn 
from the sun, with no planet to correspond 
to the number 28. It was this gap in the distances 
that led the astronomers of that day to suspect the 
existence of another planet at 2.8 times the earth's 
distance from the sun. The first asteroid discov- 
ered was at approximately 2.8 times the earth's 
48 



SPLENDORS OF THE SKY 



distance from the sun. It was found later that the 
planet Uranus, undiscovered at the time Bode's 
law was first advanced, continued the series, since 
its distance from the sun corresponds to the num- 
ber 196. The law fails, however, for Neptune. The 
planetoids are scattered throughout the entire 
space between the orbits of Mars and Jupiter. A 
few of them even come within the orbit of Mars 
and a few others are found beyond the orbit of 
Jupiter, but they occur in greatest numbers at the 
distance corresponding to the number 28 in Bode 's 
series, or 2.8 times the distance from the earth to 
the sun. 

The first asteroid was discovered by Piazzi at 
Palermo and was, by his wish, named Ceres, for the 
tutelary goddess of Sicily. A year later the astro- 
nomical world was surprised by the discovery of a 
second small planet at almost the same distance as 
the first. This was named Pallas. In 1804 a third, 
Juno, was discovered; in 1807 a fourth, Vesta. 
These four are the largest of the asteroids and their 
diameters are respectively 485, 304, 118 and 243 
miles, as determined by Barnard with the 36-inch 
telescope of the Lick Observatory. Most of the 
asteroids are much smaller. Many do not exceed 

49 



SPLENDORS OF THE SKY 



five or ten miles in diameter. After the discovery 
of Vesta in 1807 no other asteroid was discovered 
until 1845, when Hencke's long search of fifteen 
years was rewarded by the discovery of Astrsea. In 
1847 three more were discovered and from that 
time to the present, no year has passed without the 
discovery of at least one asteroid. Since 1891, 
when photography was first used for the purpose, 
planetoids have been discovered in great numbers. 
The telescope with photographic plate exposed in 
place of an observer is made to follow the stars 
for several hours. In this time the planetoid will 
move an appreciable distance. When the plate is 
developed the star images appear as clearly defined 
dots, but the asteroid has left a telltale trail upon 
the plate about a twentieth of an inch in length. 
Following the discovery a provisional designation 
is given to the object until it can be determined 
definitely whether it is a new asteroid or simply 
one rediscovered, or possibly a new comet. Wolf 's 
comet, discovered photographically in this way, was 
at first mistaken for an asteroid. New plates must 
be exposed or old plates reexamined to get addi- 
tional positions of the object from which its orbit 
is computed. Peculiarities of motion soon show 
50 



SPLENDORS OF THE SKY 



whether it is asteroid or comet or possibly a faint 
satellite of Jupiter or Saturn. 

In 1898, when astronomers were growing weary 
of their large and ever increasing family of aster- 
oids, already numbered by hundreds, and when it 
was becoming a perplexing question as to how they 
were to be named and how time could be spared 
from more urgent work to compute their trouble- 
some orbits, asteroid No. 433, known as Eros, was 
discovered. This tiny asteroid, less than twenty 
miles in diameter, has more than repaid all the 
work and trouble occasioned by the other members 
of the family and has furnished astronomers with 
probably the best method they possess for deter- 
mining the solar parallax and the dimensions of 
the solar system in miles and the distances of the 
stars and the dimensions of our whole stellar sys- 
tem as well. It is possible to determine the rela- 
tive distances of the members of the solar system 
without knowing the actual distance between any 
two of them, but we can form no idea of the extent 
of the solar system in miles and of the universe in 
light years until we actually measure the distance 
between two of the bodies. Eros comes nearer to 
the earth than any other known celestial body with 

51 



SPLENDORS OF THE SKY t 

the exception of the moon. At nearest approach 
it is only 13,500,000 miles away, and its nearness 
and clear, starlike image make it an ideal object 
for the determination of the important constant of 
the solar parallax and the distance from the earth 
to the sun, the astronomical unit of distance. Eros 
was in a particularly favorable position for obser- 
vation in the winter of 1900-1901, and a series of 
valuable observations were obtained. Thirty years 
must pass before it will be as favorably located. 
Eros aroused still further interest in 1901 when 
it was observed to vary rapidly in light. During 
February and March of that year its period of 
light variations was 2 hours 38 minutes. Its light 
at minimum was less than one-third that of maxi- 
mum. By May of the same year this peculiar 
variability had ceased. It was suggested that it 
might be explained by assuming that the planetoid 
consisted of two bodies revolving close together so 
that one body would appear to eclipse the other in 
certain positions of the orbit. According to an- 
other view the asteroid has a surface that is very 
rugged and uneven and reflects light unequally. 
In other words, like most of the asteroids, it niav 
be considered to be simply a huge rock. 
52 



CHAPTER VIII 

THE PLANETS JUPITER AND SATURN COMPARED 

WHEN the two largest planets in the sun's 
family, Jupiter and Saturn, appear in the 
heavens at the same time, as frequently happens, 
they can be readily distinguished from each other 
since Jupiter far surpasses Saturn in brightness, 
not only because it is much larger, but also because 
it is much nearer to the earth. On the date of its 
opposition to the sun, the giant planet Jupiter is 
approximately 400,000,000 miles away, while Sat- 
urn is nearly twice as far from the earth. 

The two planets closely rival each other in pop- 
ular interest. Saturn's vast system of three con- 
centric rings, more than 170,000 miles in outer 
diameter, composed of swarms of minute moonlets 
of meteoric dimensions revolving each independ- 
ently around the planet, makes it absolutely unique 

53 



SPLENDORS OF THE SKY 

in the solar system. Jupiter, on the other hand, 
on account of his satellites and belts, is by far 
the most interesting to observe of all the planets, 
as well as the largest and most imposing, and the 
one most subject to constant change and variety of 
color and markings. Though Saturn is also, beyond 
doubt, the scene of wildest tumult, its surface 
changes are rendered more blurred and indistinct 
by an additional 400,000,000 miles of intervening 
space. 

There is much similarity in the surface markings 
of the two planets, which are, in reality, phenom- 
ena of the dense enveloping gaseous strata of their 
atmospheres. Belts or bands of gaseous vapors are 
always to be seen in the atmospheres of both plan- 
ets, though the belts of Saturn are far more indis- 
tinct than those of Jupiter. They vary contin- 
ually in shade, numbers and position, but always 
lie in a direction parallel to the planet's Equator, 
being drawn into this position by the extremely 
rapid peripheral motion of the outer gaseous en- 
velopes of these planets. 

Both Jupiter and Saturn rotate on their axes in 
approximately ten hours, less than half the period 
that the earth requires to turn on its axis, though 
54 



SPLENDORS OF THE SKY 



its diameter is only about one-tenth that of the 
outer planets. 

It is an interesting and significant fact that the 
general color of the planet Jupiter fluctuates with 
the sun spot period, appearing palest when spots 
are most plentiful on the sun and more reddish as 
the frequency of sun spots decreases. This is due 
to the fact that the solar activity that produces 
sun spots also produces certain atmospheric effects 
upon the planets. It is known that high clouds, 
such as the cirrus clouds in the earth's atmosphere, 
form more readily under the solar influences that 
produce sun spots and similarly it is believed 
atmospheric changes are produced in the dense 
gaseous envelope of the giant planet. 

Marked changes are also noted at times in the 
color of the ringed planet. According to observa- 
tions made at the Lowell Observatory at the op- 
position of 1916 the planet was at that time of a 
pinkish brown color and conspicuously darker than 
its rings. 

The great distance of Saturn makes it very 
difficult to observe the finer details of its surface 
changes. It is for the same reason that Saturn's 
interesting satellite family of nine members, 

55 



SPLENDORS OF THE SKY 

exactly equal in number to that of Jupiter and 
fully as impressive in the actual size of its various 
members, arouses less interest than the family of 
the giant planet. 

Titan, the largest of Saturn's satellites, a world 
in itself, fully three thousand miles in diameter, 
can be seen readily enough with the smallest tele- 
scopes as an eighth magnitude star. Rhea, Dione 
and Tethys, whose diameters are between twelve 
hundred and fifteen hundrd miles, may also be 
seen fairly well with a four-inch telescope, which 
will also show the rings beautifully. 

Japetus, the most distant of the satellites of 
Saturn, with the exception of tiny Phoebe retro- 
grading at a distance of eight million miles, is 
almost the twin of our own moon in size. It lies 
at a distance of two and a quarter million miles 
from Saturn and requires seventy-nine days to 
make one revolution around the planet. It is of 
special interest to astronomers, owing to the fact 
that its light is conspicuously variable. "When on 
the western side of Saturn it is always brighter 
than when it is on the eastern side, and this is 
believed to be due to the fact that it always keeps 
the same face turned toward Saturn just as our 
56 



SPLENDORS OF THE SKY 



own moon always keeps the same face turned 
toward the earth. The variability of light prob- 
ably arises from a difference in the reflecting power 
of the two sides, different sides of the satellite's 
surface being turned toward the earth in the two 
positions. 

Observations made of the first two satellites, 
Mimas and Enceladus, by E. C. Slipher of the 
Lowell Observatory seem to show that these satel- 
lites also keep the same side turned toward the 
planet. They are both small bodies between 500 
and 1,000 miles in diameter that skirt rapidly 
around the outer edge of the ring system distant 
from its outer edge 30,000 and 70,000 miles re- 
spectively. 

The possessor of a small telescope will find the 
four largest satellites of Jupiter easier and more 
interesting objects to observe than Saturn's satel- 
lites. A few extremely sharp-eyed persons have 
glimpsed these four satellites with the naked 
eye, and the least optical aid will reveal them. 
Their journey ings around the giant planet and 
all the varied phenomena of the eclipses, occul- 
tations, shadows and transits can be observed with 
interest and profit by means of a three-inch tele- 

57 



SPLENDORS OF THE SKY 



scope. The five fainter satellites are beyond the 
reach of all but the most powerful telescopes, as 
are also the four smallest satellites of Saturn. 

Jupiter and Saturn resemble each other not only 
in the size of their satellite families and the nature 
of their surface markings but also in the fact that 
they are both composed almost, if not entirely, of 
matter in a gaseous state. The extremely low 
density of the two planets, less than that of the 
sun in both cases, and in the case of Saturn only 
sixty-three-hundredths that of water, the lowest for 
any planet in the solar system, contrasts sharply 
with the great density of the terrestrial planets. 
Our own planet Earth, with its surface crust and 
rigid interior, possesses a density five and one-half 
times that of water. 

The two planets, Jupiter and Saturn, are there- 
fore as different in physical constitution from our 
own world as it is possible for one to imagine. 
They possess no stable surface crust, though liquid 
and solid particles of matter may occur locally or 
be suspended in dense gaseous vapors. All is a 
whirling, seething, tumultuous mass, characterized 
no doubt by great heat, in the deeper strata at 
least, where the pressure of overlying gases must 
58 



SPLENDORS OF THE SKY 



be tremendous. A small solid or liquid core may 
exist in each planet, but the general belief is that 
both planets are almost entirely gaseous. Though 
the two planets may emit a certain amount of heat 
to their satellites, the complete disappearance of 
the satellites of Jupiter when they pass into his 
shadow shows that they receive no appreciable 
light from the huge planet other than reflected 
sunlight. 

A marked difference between these two planets 
that have so many characteristics in common is 
found in the positions of their axes of rotation with 
respect to their paths around the sun. The equator 
of Jupiter is inclined only three degrees to its orbit. 
As a result it has no change of seasons. Saturn's 
equator, on the other hand, as well as its ring 
system, which lies nearly in the same plane, is tip- 
ped twenty-seven degres to the plane of its orbit. 
This inclination of equator to orbit is the greatest 
for any planet in the solar system, exceeding that 
of the Earth by several degrees. As a result season- 
al changes on Saturn would be more pronounced 
than they are on the Earth were the effect not modi- 
fied to a great extent by the very great distance of 
Saturn from the sun. 

59 



SPLENDORS OF THE SKY 

In these two largest members of the sun's family 
we see much that is similar and much that is dis- 
tinctive. No two planets of the solar system are 
modeled exactly along the same lines. This indi- 
viduality among the various members of the same 
planet family is but a reflection of the infinite 
variety that characterizes all the wonderful form- 
ations far beyond that form a part of the same uni- 
verse to which our sun and his family belongs. 



60 



CHAPTER IX 

SATURN THE RINGED PLANET 

OF all the brighter planets Saturn is the least 
interesting to observe with the naked eye and 
one of the most interesting viewed through the tele- 
scope. 

It shines with a dull leaden light, very different 
from the fiery red of Mars, the sparkling beauty 
of Venus, or the splendor of Jupiter. 

Saturn is usually spoken of as the ringed planet 
and is unique in the solar system for several rea- 
sons. It is the only planet that is lighter than 

water, the only one that would float if thrown 

9 
into a body of water large enough to contain it, 

and it is surrounded by a system of rings of mar- 
velous appearance. 

There are three of these thin, flat, concentric 
rings, two bright ones and a third called the dusky 

61 



SPLENDORS OF THE SKY 



or crepe ring. Tlie outer ring, which is called 
"A," has an exterior diameter of 173,000 miles 
and a width of 11,000 miles. It is separated from 
"B," which is much brighter, By a division of 
2,200 miles of uniform width all around known as 
Cassini's Division. The third or dusky ring, "O," 
was discovered in this country in 1850 and is com- 
paratively hard to see. Its width is equal to that 
of the outer ring and its inner edge is only 6,000 
miles from the surface of the planet. The ring' ' B ' ' 
is about 18,000 miles wide. The thickness of the 
ring system is less than 100 miles and its weight 
is next to nothing. ''Immaterial light" the rings 
have been called by the astronomer Struve. They 
are of perfect symmetry and when seen in a 
telescope fill the observer with admiration and 
awe. 

As to composition, they are now known to be 
3warms of tiny satellites or moons, nothing more 
than meteors in size, and they are in constant 
revolution around Saturn. Every 15 or 17 years 
the rings entirely disappear from view for a 
short time even in the most powerful telescopes. 
This is due to the fact that once every 15 or 17 
pears the earth is exactly in the plane of the rings 
62 



SPLENDORS OF THE SKY 



and the edge of the rings is directly in the line of 
sight. This causes the entire disappearance of 
the rings from our point of view. The next dis- 
appearance wiil occur in 1922. 

For the remaining time the earth is either above 
or below the plane of the rings and we either 
look down upon them from above or up from be- 
neath, as the case may be, and so see them at vary- 
ing widths. 

In addition to the rings Saturn has nine satel- 
lites, and the outermost is at a distance of about 
8,000,000 miles from Saturn. So extensive is this 
vast system, truly a solar system in miniature ! The 
names of the satellites in order of distance outward 
from Saturn are Mimas, Enceladus, Tethys, Dione, 
Rhea, Titan, Hyperion, Japetus and Phoebe. By 
far the largest of these is Titan, which is of the 
same size as the planet Mercury. 

The most remarkable of the satellites is Phoebe, 
because, while all the other satellites of Saturn 
follow the usual direction of revolution in the solar 
system and revolve from west to east around their 
primary, Phoebe revolves from east to west or 
retrogrades, as it is called. 

The periods of revolution of the satellites around 
63 



SPLENDORS OF THE SKY 



their primary show great diversity, ranging from 
22!/2 hours for Mimas, which skirts along the outer 
ring, to 16 months for Phoebe, the most distant 
of all. In shape Saturn is the most flattened at 
the poles of any of the planets. It is decidedly 
oval in appearance. This is very noticeable at the 
time of disappearance of the rings, when we get an 
unobstructed view of Saturn's globe. Saturn also 
has belts, similar to those of Jupiter, but fainter in 
color and more indistinct. 

Both of these planets are apparently in a much 
earlier stage of development than the earth. Saturn 
is a world in a state of chaos, and the dense can- 
opy of clouds, with which it is surrounded, points to 
a surface of intense heat, for Saturn is too far from 
the sun to have its clouds raised by solar heat. 
They must be the product of its own seething heat. 
This is a world in the making and the dense 
clouds with which it is surrounded will probably 
settle down upon its surface as oceans in ages 
to come. 

It is hard for us to realize as we look upon this 

planet of leaden hue, not so much brighter than a 

first magnitude star, so great is its distance from 

us, that in size our earth compares with it as a 

64 



SPLENDORS OF THE SKY 



pea with an orange, and that, as the celebrated 
French astronomer Flammarion has said, the earth 
might roll upon the ring system like a ball upon 
a road. 



65 



CHAPTER X 

PLAIN FACTS ABOUT THE MOON 

ALL the planets in the solar system, with the 
exception of Mercury and Venus, are at- 
tended by satellites. Saturn has nine, in addition 
to his ring system, composed of numberless tiny 
moonlets. 

Jupiter also has nine moons, Uranus four, Mars 
two and Neptune one, while our own planet, Earth, 
has a satellite which is in one respect unique in the 
solar system. The ratio of its size to that of its 
primary far exceeds that of any other satellite. 
Its dimensions are quite comparable with those of 
the earth. Its diameter is about 2,160 miles. The 
earth's diameter is about 7,900 miles. 

Fifty moons would equal the earth in volume, 
although it would take eighty-one times the mass 
of the moon to equal the mass of our planet, as 
fifi 



SPLENDORS OF THE SKY 



the lunar density is only six-tenths that of the 
earth. The entire surface of the moon about equals 
North and South America in area, though about 
forty per cent, of its surface we can never see, since 
our satellite always turns the same face toward us. 

Titan, the largest satellite of Saturn, has a 
diameter of 3,500 miles, and is larger than the 
planet Mercury, but it would take 4,600 Titans to 
equal Saturn in mass. Ganymede, the largest 
satellite of Jupiter, is almost exactly of the same 
size as Titan, but its mass must be increased 11,000 
times to equal that of Jupiter. 

Neptune's moon about equals our own in size, but 
is a very tiny object compared with its primary, 
which has a diameter of 35,000 miles. The largest 
of the satellites of Uranus is only 1,000 miles in 
diameter and the two tiny moons of Mars average 
about ten miles in diameter. 

Our own satellite is a most beautiful and inter- 
esting telescopic object and even when viewed with 
an opera glass, its apparent distance is reduced 
one-half. With moderate sized instruments we 
may view it at an apparent distance of about 1,000 
miles. The greatest telescopes make it appear only 
sixty miles away, but we must remember such a 

67 



SPLENDORS OF THE SKY 



view is by no means clear and distinct, for atmos- 
pheric imperfections are magnified as well. 

Even with moderate sized instruments, how- 
ever, any lunar object a mile or so in diameter 
is readily discernible, and with large instruments 
and a trained eye and good atmospheric condi- 
tions, any object a quarter of a mile in diameter 
could be detected. If large cities existed upon the 
moon very moderate instruments would show them. 

The question of life upon the moon is readily 
disposed of, for we know that there is neither air 
nor water there. The moon's period of rotation 
upon its axis is equal to its period of revolution 
around the earth. In other words, it always turns 
the same face toward the earth and its day is two 
weeks long. Fourteen days of light are followed 
by fourteen days of darkness. 

During the lunar day the barren surface of the 
moon is exposed to the intensity of the solar rays, 
unmitigated by any protecting atmosphere. The 
temperature must rise during this scorching period 
as high as the boiling point, to fall during the long, 
dark night that follows nearly to the absolute zero 
of interplanetary space. 

Because of the absence of an atmosphere upon 
68 



SPLENDORS OF THE SKY 



the moon there is no diffusion of light. Shadows 
are inky black and the stars above shine by day 
and by night, in an inky sky. Stars that we need 
a field glass to see upon the earth would be readily 
seen with the naked eye upon the moon. The 
Milky Way, so dimly seen by us, is a gorgeous 
spectacle in the lunar heavens. The solar corona 
and prominences are always visible, as is also the 
zodiacal light. The planet Mercury, so elusive to 
our eyes, is easily observed from the moon. Both 
stars and planets shine far more brilliantly there 
against a background that is always black. 

As regards the lunar landscape, even the small- 
est telescope shows us many features not visible to 
the naked eye. Extensive dark and light regions 
give our satellite its spotted appearance. The light 
portions are always rough and the dark ones com- 
paratively smooth. The latter have been incor- 
rectly termed maria or seas ever since the time of 
Galileo, who believed these grayish patches were 
really vast expanses of water. They are designated 
by such fanciful names as Sea of Clouds. Sea of 
Serenity, Lake of Dreams, etc. 

The most distinctive lunar features are the 
craters, numbered by the thousands, and possibly in- 

69 



SPLENDORS OF THE SKY 

correctly named, for we naturally think of a crater 
as formed by volcanic action and it is by no 
means certain that the craters of the moon are 
of volcanic origin, though this belief is still held 
by some astronomers. 

The larger craters, which are often from fifty 
to one hundred miles in diameter, are usually com- 
paratively shallow, about three miles or less in 
depth. Frequently a single mountain a mile or so 
in height rises from the centre of the crater, or 
ringed plain, as it is often called. It has been 
estimated that there must be fully 100,000 craters, 
ringed plains and craterlets upon the surface of 
our satellite. It is these formations that make its 
face appear so pockmarked and scarred. 

A conspicuous crater, visible even to the naked 
eye, is Tycho, often called "the metropolitan crater 
of the moon." It lies near the south pole of the 
moon, has a diameter of over fifty miles and is 
nearly 17,000 feet deep. It has a central hill 6.000 
feet high and is a typical lunar crater. 

The moon is also remarkable for its systems of 

rays or streaks radiating from prominent craters. 

These extend for vast distances, nearly 2,000 miles 

in one instance. Those surrounding Tycho emanate 

70 




THE MOON AGE, 8}4 DAYS 

(Photographed by Ritchey at the Yerkes Observatory) 



SPLENDORS OF THE SKY 



from it like brilliant lines of longitude. They 
appear to be neither elevated nor depressed, but 
run in remarkably straight lines over hill and plain 
interrupted by no feature of the lunar landscape. 

These rays still remain one of the riddles of the 
moon, though, according to those who believe in 
the meteoric origin of the moon they were caused 
by the splashing of some light colored material 
when an unusually large meteor struck the lunar 
surface. Supporters of this belief point also to 
the fact that large deposits of sulphur upon the 
moon's surface have been photographed in ultra- 
violet light. 

A number of craters are surrounded by these 
streaks. Copernicus, a crater a little northeast of 
the centre of the moon's disk, has a remarkable 
system of feathery streaks. 

Clefts, or rills, as they are called, are also seen 
in large numbers upon the moon. They are often 
more than 100 miles long, but are usually extremely 
narrow, often mere cracks in the surface, half a 
mile or so wide. Mountain chains also exist upon 
the moon similar to mountain chains upon the 
earth. There are the lunar Alps and Appenines, 
with peaks running up to 20,000 feet in height. 

71 



SPLENDORS OF THE SKY 



On the extreme southern edge of the disk are two 
mountain chains spoken of by the French astrono- 
mer Flammarion as the " mountains of eternal 
light/' for the sun never sets upon these peaks, 
one of which is 7,000 feet higher than Mount 
Everest. 

From the moon the earth appears about thirteen 
times as large as the moon does to us. Seen from 
any point upon the visible lunar disk it would 
appear practically immovable in the sky, its alti- 
tude varying for different positions on the moon's 
surface. The diurnal rotation of the earth would 
be clearly seen, as would also its continents and 
seas, polar caps, mountains and plains, its clouds 
and storms. It would exhibit all the phases that 
the moon does to us in reverse order. 

Many theories of the origin of the moon have 
been advanced, but all seem to present some diffi- 
culties. Our satellite furnishes us many unsolved 
problems. A belief in the meteoric origin of the 
moon is now quite general. According to this be- 
lief the earth was surrounded in the early stages 
of its existence by a ring of meteoric matter. The 
material forming the ring gradually gathered into 
one mass, our present moon, whose pitted face gives 
72 



SPLENDORS OF THE SKY 



evidence of the bombardment it received from 
meteoric masses within the ring". 

According to this theory our satellite has always 
been a dead world, a cold and lifeless mass of 
meteoric rock. It has never felt the pulse of life 
or undergone the mighty changes that have passed 
over its ruling planet, the Earth. It has remained 
a cold and silent witness to vast evolutionary proc- 
esses going on upon a neighboring world such as it 
could never experience for itself. 



73 



CHAPTER XI 

SOME UNSOLVED PROBLEMS OF THE MOON 

A MOST troublesome little member of the sun's 
* *■ family is our satellite, the moon. The nearest 
to the earth of all the heavenly bodies and the most 
easily observed, the moon presents as many un- 
solved problems as the stars themselves. 

There are more theories advanced to explain 
the origin of the lunar craters than there are to 
explain the nature of the "canals" of Mars. We 
hear many conflicting theories. First there is the 
theory of a terrific explosion from within and the 
resulting deluge of the lunar surface with an out- 
flow of highly heated material of spongy consist- 
ency with its bursting bubbles of gas, to be fol- 
lowed later by secondary explosions and more 
deluges. Then there is the opposite theory of in- 
tense bombardments by meteorie masses from with- 
74 



SPLENDORS OF THE SKY 



out that have disfigured and pitted the face of our 
satellite. 

There is also the theory that the moon was once 
a part of the earth and that the two gradually- 
separated and the distance between them increased 
slowly under the complicated action of tidal forces 
exerted by the sun as well as by the earth and 
moon. And there is another theory that the moon 
never was a part of the earth but has been captured 
by our planet. 

There is one problem presented by irregularities 
in the motion of the moon that transcends all other 
lunar problems in importance. Indeed, it may 
lead to discoveries bearing on the nature of gravi- 
tation itself. It has long been known that the 
motion of the moon is not in keeping with the 
theory. The observed positions of the moon are not 
in good agreement with the computed positions and 
since the theory has been carried to a high degree 
of accuracy it is now suspected that the difference 
is due to the action of some unknown law that may 
be as fundamental as the law of gravitation. 

The positions of most of the members of the 
solar system can be computed over an interval of 
a number of years, according to the law of gravi- 

75 



SPLENDORS OF THE SKY 

tation, with such a high degree of accuracy that the 
observed and computed positions are practically 
identical. The same cannot be said of the moon, 
however. For half a century or a century the moon 
will revolve around the earth a little ahead of its 
regular rate and then for another long period of 
time will gradually fall behind. Empirical cor- 
rections are constantly being applied to the moon's 
position in order to bring the observed and pre- 
dicted positions into agreement. 

So complicated is the theory of the moon that 
only astronomers possessing the highest mathe- 
matical ability are fitted to cope with it. Noted 
mathematicians and astronomers have spent years 
of effort in trying to discover the cause of the large 
and continually increasing discrepancies between 
the predicted and observed positions of the moon. 

New tables for computing the position of the 
moon have recently appeared. They are the result 
of years of work by Prof. E. "W. Brown of Yale 
University, one of the best known theoretical 
astronomers of the present day, and a number of 
assistants. It is believed that these tables give the 
moon's position with as high a degree of accuracy 
as it is possible to obtain it by taking account of 
76 



SPLENDORS OF THE SKY 



all known factors affecting the motion of our satel- 
lite. Nevertheless, positions of the moon computed 
with the new tables do not agree with the ob- 
served positions, and it is evident that there is some 
unknown factor in operation that is affecting the 
motion of the moon. 

Comparisons of the observed with "the predicted 
times of beginning and ending of totality in total 
eclipses of the sun by the moon show the amount 
of error in the computed position of the moon at 
the time of the eclipse. 

It was found in 1900 that the predicted time of 
the beginning of the total eclipse was seven seconds 
too early and the path of the moon's shadow upon 
the earth was consequently a mile or two in error. 
In 1905 astronomers were surprised to find the 
difference had increased to twenty seconds, and in 
the total eclipse of June 8, 1918, the predicted time 
would have been in error eighteen seconds if a cor- 
rection had not been applied shortly beforehand, 
which reduced the amount of the error almost to 
zero. 

This correction was found from recent observa- 
tions of occultations of stars by the moon. Since 
the positions of the stars can be obtained with a 

77 



SPLENDORS OF THE SKY 



high, degree of accuracy the true position of the 
moon can be found for the time when the star is 
occulted or hidden behind the disk of the moon. 
Observations of eclipses and occultations are used 
to correct the tables that are used to predict the 
moon's position from year to year, but these cor- 
rections are empirical and it is not known yet to 
what they are due. 

It will be remembered that an unexplained 
error in the computed positions of Uranus finally 
led to the discovery of the planet Neptune, which 
was producing the deviations in the predicted places 
of this planet. The irregularities in the moon's mo- 
tion cannot be attributed to an undiscovered planet, 
however, and there is a strong possibility that there 
may be something in the nature of gravitation itself 
that is producing the discrepancies. 

According to a theory that has been recently ad- 
vanced by Prof. See of the Naval Observatory at 
Mare Island, Cal., gravitation is to be considered 
as an electro-magnetic force. He believes that the 
unexplained deviations in the moon's position are 
caused by the refraction, dispersion and absorption 
of some of the magnetic forces of the sun by the 
earth at the time of full moon and more especially 
78 



SPLENDORS OF THE SKY 

at the time of the eclipse of the moon by the earth. 
It appears that this explanation may account for 
one of the unknown terms but it does not account 
for all of them. 

It may happen that when the cause of the errors 
in the moon's computed positions is found a funda- 
mental law of the universe will be discovered as 
well. It is in just this way that many valuable and 
important discoveries are made. The velocity of 
light was discovered while attempts were being 
made to explain errors in the computed times of the 
eclipses of Jupiter's satellites. Bradley made sev- 
eral very important discoveries, such as the aberra- 
tion of light and the nutation or wabbling of the 
earth's axis that affects the positions of all the 
stars, while he was attempting to measure the dis- 
tances of the stars. So it will be by no means sur- 
prising if our troublesome little moon some day 
figures in a very far reaching discovery. 

The moon's attraction for the earth gives rise 
to the tides so familiar to every one. The sun also 
produces tides upon the earth, but as the sun is so 
much further away its tide raising forces are 
inferior to those of the moon. 

A small amount of light and heat is reflected 
79 



SPLENDORS OF THE SKY 

from the moon to the earth and there are 
minute variations in the position of the magnetic 
needle to be attributed to the moon's influence, 
as well as some minor changes in the earth's motion. 
Aside from this the moon does not affect in the 
least conditions existing upon the earth, though 
there is no other heavenly body that is associated 
with more superstitious beliefs. 

To follow the course of the moon through the 
heavens during one month, the period of its revo- 
lution around the earth, and to explain the cause 
of its various phases is a very elementary matter, 
yet it appears to be a most perplexing problem for 
nearly every one. In the present age, when astro- 
nomical knowledge is so easily obtained, artists still 
delight in placing the crescent moon overhead at 
midnight, an astronomical blunder as serious as 
picturing the sun in the west early in the morning. 
Less frequently the horns of the crescent moon are 
turned toward the horizon, though a moment's 
thought would demonstrate the absurdity of this 
position if the cause of the moon's phases is at all 
understood. A most woeful lack of knowledge, 
either of the cause of the phases of the moon or of 
the relative distances of the stars and the moon, 
80 



SPLENDORS OF THE SKY 



is evidenced when a star is pictured between the 
horns of the crescent moon. 

A knowledge of the elementary facts concerning 
the moon and its motion is as easily acquired as is 
the knowledge of the cause of the rising and setting 
of the sun and the changing seasons, and it seems 
quite unbelievable that there should be widespread 
ignorance of such simple, yet fundamental, matters. 



81 



CHAPTER XII 

SHOOTING STARS AND METEORS 

UNTIL the beginning of the nineteenth century 
it was deemed an absurdity to believe that 
stones fell to earth from the heavens. Such rumors 
had persisted for centuries, but they were attrib- 
uted to the ignorant and superstitious. 

Finally, in the year 1803 man was compelled to 
change his views somewhat suddenly; not in some 
far away corner of the earth, but over an extent of 
many miles in thickly populated districts of France 
thousands of such stones fell in a single day. 
Their appearance was accompanied by the sharp 
reports and detonations now known to be always 
attendant upon the passage of meteorites through 
the earth's atmosphere. 

Scientists sent to the district by the French In- 
stitute heard accounts of the phenomenon as seen 
82 



SPLENDORS OF THE SKY 



by hundreds of eye witnesses and brought back 
many of the stones. 

After man's mind was open to conviction it was 
found that the fall of meteoric stones from the 
heavens was by no means a rare occurrence, though 
their appearance in such large numbers as had 
been observed in France in 1803 was unusual. It 
has been concluded from a conservative estimate 
that the number of large meteorites or aerolites that 
reach the earth yearly must approximate fully one 
hundred in number. 

This estimate includes also those that fall in un- 
inhabited lands or into the large bodies of water 
that cover three-fourths of the earth's surface. In 
addition to the meteorites that weight anywhere 
from a few pounds to several tons, it has been esti- 
mated from extensive observations that between 
ten and twenty million meteors or shooting stars 
enter the earth's atmosphere daily. Their average 
weight is considerably less than an ounce and they 
are usually consumed by the friction produced by 
their rapid flight through the air. The resulting 
dustlike particles float in the air or gradually settle 
to the earth's surface, adding to its mass a few 
tons daily. 

83 



SPLENDORS OF THE SKY 



Though this seems to be a considerable amount, 
it is so small in proportion to the earth's total mass 
that it would not become appreciable for many 
hundreds of thousands of years. These meteors 
are believed to be the debris of comets encoun- 
tered by the earth in its journey around the sun. 
If the earth is continually encountering meteoric 
dust, so, doubtless, are all the other planets as 
well, and the total amount within the solar system 
must be very considerable. 

Astronomers are now giving a good deal of at- 
tention to the question of the scattering of light 
by cosmical dust throughout the universe at large 
and there are indications of the presence in our 
own solar system of appreciable quantities of finely 
divided matter. 

Interplanetary space is by no means a void. 
Tails of comets appear at times to be brushed aside 
or cut off in a manner quite unaccountable, unless 
we assume that some resisting medium has been en- 
countered such as would present no difficulty to 
a larger mass, satellite or planet, but becomes very 
disturbing to such tenuous matter as the tails of 
comets. 

The motion of Mercury is not just as it would be 
84 



SPLENDORS OF THE SKY 

^^mm ^ mmmmmmmmmmm — »■■■■■ ^ ■■ ■■■■ i^ ■■■■■■■■ 

if affected only by the attraction of the known 
planets. This has led to the suspicion that there 
may be one or two small intra-mercurial planets, 
and they have been searched for diligently at times 
of total eclipse of the sun, so far unsuccessfully. 
Some astronomers believe, however, that finely di- 
vided particles of matter existing in the Zodiacal 
Light may account for the peculiar behavior of the 
innermost planet. 

After sunset in the spring or before sunrise in 
the fall, when the ecliptic rises most sharply from 
the horizon, the careful watcher may see a faint 
wedge of light, about equal in brightness to the 
Milky Way, extending from the horizon to the 
zenith. Near the horizon it is fully twenty degrees 
wide, but it rapidly narrows to a width of three 
degrees or four degrees overhead. Under favor- 
able conditions it can be traced far beyond the 
zenith. This is called the Zodiacal Light and ex- 
actly opposite the sun also appears at times a faint 
oval patch of light covering an area about the size 
of the bowl of the Big Dipper. This is the Counter- 
glow, and it is so excessively faint that few have 
ever observed it. 

Both Zodiacal Light and Counter-glow are un- 
85 



SPLENDORS OF THE SKY 



observable if there is any moonlight. It is be- 
lieved that the Zodiacal Light is due to reflected 
sunlight from a great number of finely divided 
particles circulating around the sun in the plane 
of the earth's orbit and extending even beyond the 
earth. The Counter-glow is not so easily explained, 
but it probably represents a condensation of these 
particles at some point beyond the earth's orbit at 
a point about 930,000 miles from the earth and 
just beyond the reach of its shadow where the com- 
bined forces of the earth and sun would cause mat- 
ters to be drawn into a sort of whirlpool of mo- 
tion. Sunlight shining upon these particles makes 
them visible to us when directly opposite the 
sun. 

So it appears that cosmical dust and fragment- 
ary matter is fairly plentiful within our solar 
system. Probably a large amount of such meteoric 
dust is swept up by the larger planets as they jour- 
ney around the sun, but the supply is also replen- 
ished by the escape of particles of matter from the 
atmospheres of sun and planets. 

The sun is the seat of intense activity and ex- 
plosive agents are at work there that cause flames 
of the lighter gases to shoot forth at times to 
86 



SPLENDORS OF THE SKY 



heights of more than 300,000 miles with velocities 
of about two hundred miles or more per second. A 
velocity of more than three hundred and eighty- 
miles per second would enable particles of matter to 
permanently escape from the control of the sun and 
pass to space beyond. Light pressure acting upon 
small particles of matter may also overbalance the 
sun's attraction and drive cosmical dust away from 
the vicinity of the sun. The corona, we know, is 
partly composed of dust particles and liquid glob- 
ules shining by reflected sunlight as well as light 
of incandescence. 

Most interesting of all fragmentary matter ex- 
isting within our solar system are the meteorites 
previously mentioned. There are several theories 
concerning the origin of these peculiar stones. The 
idea that they are simply larger portions of dis- 
rupted comets is quite generally held, and yet 
these stones rarely appear when showers of meteors 
are experienced. They almost invariably appear 
singly. 

The fact that they contain no unknown elements 
and in some respects resemble lava from deep vol- 
canoes led to the old belief that they were expelled 
from the interior of the earth or other planets by 

87 



SPLENDORS OF THE SKY 



intense volcanic activity in the past and after re- 
ceding to great distances returned and fell once 
more within reach of the earth's attraction. This 
belief leaves unexplained many of the characteris- 
tics of meteorites. Volcanic action intense enough 
to overcome the effect of the earth's attraction 
would cause a fusion of the material of which the 
meteorites consist such as does not appear. 

In some few instances meteorites are composed 
of nearly pure iron, but usually they are frag- 
ments of stone with peculiar crystals and consid- 
erable quantities of gases that are sometimes com- 
bustible, hidden in their crevices. They usually 
show none of the results of the action of water and 
very little oxidation. Some show veins where for- 
eign substances have been slowly deposited and 
signs of fracture and sliding of one surface on an- 
other. 

The most interesting theory respecting these vis- 
itors from the heavens is that they are fragments 
of disrupted bodies, possibly of planetary dimen- 
sions, that at some time chanced too near a larger 
mass and were torn asunder under tidal stress and 
strain. 

It is even a possibility that the solar nebula, 
88 



SPLENDORS OF THE SKY 



from which we believe our present solar system 
was fashioned, originated in the close approach of 
two suns and that around one or both of these suns 
at that time planets were circling. The tremendous 
tidal reaction between the two suns would result 
in streams of matter being ejected and the forma- 
tion of a spiral nebula. 

If planets encircled these suns they would be 
completely shattered and scattered as meteoric 
fragments. The larger nuclei of ejected matter 
would gradually increase in size by sweeping up 
other fragments of matter and become the chief 
planets of another system. Smaller nuclei in the 
vicinity of larger ones would form the satellites 
attendant upon the planets. The eight hundred or 
more asteroids may represent smaller independent 
masses that have avoided collisions, while comets 
and meteors are the debris remaining when order 
has finally been brought out of chaos. 

During the course of millions of years all frag- 
ments of considerable size would be captured by 
the major planets and satellites. In fact, the scans 
on the face of our satellite, many believe, are due 
to terrific meteoric bombardment in the past. Ac- 
cording to this latest theory of the possible origin 

89 



SPLENDORS OF THE SKY 



of meteorites, fragments of worlds antedating our 
own may fall to the earth's surface every year by 
scores, and in a few cases find their way into our 
museums. 



90 



CHAPTER XIII 

OUR CELESTIAL VISITORS, COMETS 

THE number of comets that are observed and 
recorded is enormous, but most of these are 
telescopic and conspicuous comets are few. Hardly 
a year passes without the appearance of several of 
these mysterious visitors. Some of these comets 
are old friends returning, periodic comets that ar- 
rive more or less on schedule time, while others 
that travel in greatly elongated ellipses only ap- 
proach the sun once in hundreds or even thousands 
of years. Donati's great comet of 1858 takes 2,000 
years to complete its circuit. It is a question 
whether some comets ever return to the solar re- 
gions again, for their orbits appear to be parabolic 
rather than elliptical. Since, however, we can ob- 
serve only a very small portion of the orbits of 
some comets that penetrate far into the depths of 

91 



SPLENDORS OF THE SKY 



space beyond the orbit of Neptune and since the 
arc of both ellipse and parabola are nearly coin- 
cident for the short interval of observation we are 
left in doubt as to whether all comets return or not. 

Some may speed forth into the immensity of 
space that separates our solar system from the 
stars beyond never to return, but there are com- 
ets in great numbers that are known to be per- 
manent members of the solar system, and that ac- 
company it on its onward journey through space. 
They encircle the sun in orbits that are greatly 
elongated ellipses markedly different from the 
nearly circular orbits of the planets. 

If a comet on its journey around the sun passes 
close to one of the major planets, it may come 
under the gravitational influence of that planet to 
such an extent that its path will be entirely 
changed and its aphelion or the point of its orbit 
furthest away from the sun will afterward lie close 
to the orbit of that planet. Jupiter has a family 
of about thirty comets. His family is the largest 
because his mass is greater than that of all the other 
planets combined. All the aphelia of these cap- 
tured comets, of course, lie near Jupiter's orbit. 
Neptune has a family of six comets. 
92 



SPLENDORS OF THE SKY 



There are two or three groups of comets whose 
aphelia lie at distances several times as great as 
Neptune's distance from the sun, and possibly fu- 
ture investigations of cometary orbits of long pe- 
riod may lead to the discovery of several trans- 
Neptunian planets. There is no reason to suppose 
that Neptune is the farthest planet from the sun, 
for the gravitational influence of the sun extends 
enormously beyond it. 

Comets of short period are usually spoken of as 
periodic comets. The shortest period, three and 
one-third years, is that of Encke's comet, which, 
when furthest from the sun, never gets beyond the 
orbit of Jupiter, while Halley's noted comet, which 
made its last return in 1910, has the longest period 
of comets classed as periodic. No great or con- 
spicuous comet belongs to this class. 

Though comets are the bulkiest of all heavenly 
bodies, they are also possessed of the least mass of 
any known bodies that travel through space. Com- 
ets usually consist of a nucleus, coma or head, and 
tail. The nucleus, which in great comets fre- 
quently appears as bright as first magnitude stars, 
is no more than a swarm of meteoric particles. Of 
the actual size of the particles we can form no 

93 



SPLENDORS OF THE SKY 



idea, but they are evidently held together by a 
very loose bond of gravitation. The entire nucleus 
is enwrapped in a gaseous envelope that forms the 
head of the comet. This coma or head is often of 
enormous dimensions. The head of Donati's comet 
was 250,000 miles in diameter, while the head of 
the comet of 1811 measured over 1,000,000 miles 
at one time. As the comet approaches close to the 
sun the head is observed to contract or diminish in 
size. 

The tail, which is the most noticeable and dis- 
tinctive feature of a comet, does not develop until 
it draws in toward the sun. It then becomes, in 
many cases, millions of miles in length. The Great 
Comet of 1843 had a tail more than 200,000,000 
miles in length and the comet of 1882 had a head 
200,000 miles in diameter and a tail 100,000,000 
miles long. These two comets, as well as the great 
comet of 1880, pursued nearly identical paths. All 
three were noted for their close approach to the 
sun. The comet of 1843, in fact, passed through 
the corona and within 32,000 miles of the sun's 
surface, and only its enormous velocity of several 
hundred miles per second saved it from actually 
falling into the sun. Its enormous tail appeared 
94 




BROOKS' COMET 

(Photographed by Barnard at the Lick Observatory) 



SPLENDORS OF THE SKY 

to be whirled around the sun in about two hours 
and this fact proved conclusively that the tail could 
not be an actual appendage, but must be a series 
of emanations from the head due either to the elec- 
tric repulsion of the sun acting upon highly rare- 
fied material in the head of the comet or to light 
pressure which overbalances the effect of gravity 
in the case of particles of extremely small mass. 

Comets shine not only by reflected sunlight, but 
by inherent light as well, and the spectroscope 
shows that they are composed chiefly of gaseous 
compounds of hydrogen and carbon, though when 
near the sun metallic lines of sodium and iron fre- 
quently appear. So highly rarefied is the material 
composing the heads and tails of comets that faint 
stars are often observed to shine through them 
undimmed, even when close to the nucleus. The 
fact that the earth has many times been involved 
in the tails of comets with no disastrous conse- 
quences — in fact, without our knowing it until 
later — shows the flimsy nature of these appendages. 
If the earth should meet a comet head on, how- 
ever, it would doubtless experience a more or less 
severe meteoric shower, depending upon the size 
of the meteoric stones within the nucleus. 

95 



SPLENDORS OF THE SKY 



Continued returns of periodic comets to the vi- 
cinity of the sun tend to reduce them greatly in 
size and brilliancy and it is for this reason that 
none of the short-period comets are as striking or 
conspicuous objects as the great comets of long 
periods and infrequent returns. Even Halley's 
comet, the largest and most noted of periodic com- 
ets, was a decided disappointment as a "show" 
comet upon its return in 1910. Meteoric showers 
are composed of the debris of comets that have be- 
come disintegrated, and comets have been seen to 
separate into two or more branches. Many comets 
travel in groups along the same curve. The great 
comets of 1843, 1880 and 1881 belong to such a 
group. They follow practically the same path and 
may have even formed one enormous comet at some 
time in the past. 

It is not so many years since the visits of these 
mysterious strangers were received with dread and 
fear, for it was believed that they predicted evil, 
either war, famine, pestilence or death of royalty. 
Needless to say, such fears were entirely without 
foundation, but so superstitious are the masses that 
even to the present day traces of these beliefs still 
linger. In 1910 when Halley's comet made its 
96 



SPLENDORS OF THE SKY 



predicted return, Chinese mobs attempted to 
frighten away the unwelcome visitor with flaring 
torches. If a great and conspicuous comet had 
made a sudden appearance just prior to August, 
1914, we might have found that "civilized" west- 
ern nations, even in this age, are not so entirely- 
free from superstitious fear concerning unusual 
heavenly phenomena as we might like to believe. 



97 



CHAPTER XIV 

HOW CARBON DIOXIDE IN THE EARTH 'S ATMOSPHERE 
AFFECTS CLIMATE 

\ C CORDING to the scientists, man's extrava- 
■* *- gant consumption of coal may, in the course 
of a very few centuries, materially affect the com- 
position of the atmosphere and thereby the average 
yearly temperature at the earth's surface and cli- 
matic conditions. 

Carbon dioxide, which is the product of the com- 
bustion of coal, is one of the constituents of the 
atmosphere. The amount of this compound found 
in the atmosphere is extremely small, three-hun- 
dredths of one per cent, by volume, five-hundredths 
of one per cent, by weight. Although the percent- 
age of carbon dioxide is so small it has an appreci- 
able effect upon the earth's climate. 

The amount of coal mined and burned annually 
98 



SPLENDORS OF THE SKY 



is approximately one billion tons, and as a result 
of this combustion a little over three and a half 
billion tons of carbon dioxide are added yearly to 
the present amount of carbon dioxide in the earth's 
atmosphere, which is approximately three trillion 
tons. 

A simple computation will show that the amount 
of carbon dioxide in the atmosphere will be doubled 
in about eight hundred years if the present rate 
of combustion of coal is maintained. 

The absorbing properties of carbon dioxiae are 
practically the same as those of water vapor. The 
intensely hot rays of the sun of shortest wave 
length, those from the blue end of the spectrum, 
pass through the carbon dioxide and water vapor 
in the air as readily as through nitrogen and oxy- 
gen, the chief constituents of the atmosphere, but 
the longer heat rays, as they are called, from the 
red end of the spectrum suffer strong absorption 
by the carbon dioxide and water vapor in the 
earth's atmosphere. 

The radiations from the earth's surface are com- 
posed almost entirely of the rays of longer wave 
lengths and are, therefore, largely absorbed by 
these compounds. The blanketing effect of the at- 

99 



SPLENDORS OF THE SKY 



mosphere is greatly increased by the presence of 
water vapor and carbon dioxide. It has been esti- 
mated that fully thirty-five per cent, of the sun's 
rays that enter the atmosphere of the earth per- 
pendicularly are absorbed before they reach the 
surface of the earth. 

At night the heat absorbed by the atmosphere 
during the daytime is radiated in all directions and 
portions of it strike the earth's surface directly 
and warm it, while other portions are reflected 
back to the earth from the upper atmosphere. Also 
the heat rays radiated from the earth's surface 
during the night are trapped by the water vapor 
and carbon dioxide in the atmosphere and raise 
the temperature of the air. 

As a result the extremes of temperature be- 
tween day and night are greatly reduced by the 
presence of these two compounds in the atmos- 
phere. 

Every one is aware of the fact that on the moun- 
tain heights where the atmosphere is less dense the 
days are hotter and the nights colder than they 
are at sea level. It is also well known that the 
early autumn frosts occur only when the air is 
clear and the amount of water vapor in the atmos- 
100 



SPLENDORS OF THE SKY 



phere small. An increase in the amount of carbon 
dioxide in the air would have the same effect on 
the temperature as an increase in the amount of 
water vapor, since the heat absorbing properties 
of the two are the same. 

Certain geologists believe that the amount of car- 
bon dioxide in the earth's atmosphere has varied 
periodically over long intervals of time and that 
the glacial periods and the warm periods that have 
occurred alternately in the past have been due to 
this variation in the composition of the atmosphere. 
The effect of an increase in the amount of carbon 
dioxide in the earth's atmosphere is to increase the 
general temperature of the air, while a decrease 
in the amount of carbon dioxide lowers the sur- 
face temperature of the earth. 

The enormous amount of coal burned by the 
human race yearly will, therefore, in the course of 
time, increase the earth's temperature and affect 
the climate throughout the world. Whatever af- 
fects the nature or direction of the air currents 
that flow over the earth's surface will possess the 
greatest influence over the general temperature of 
the world, for to the air currents and their equal- 
izing effect upon the climate is to be attributed the 
101 



SPLENDORS OF THE SKY, 



habitability of both the polar and tropical regions 
of the earth. 

The composition of the atmosphere has the great- 
est influence over the forms of life existing upon a 
planet, and in considering the question of life on 
other planets the nature and composition of the 
atmosphere is first in importance. 

It is extremely difficult to speculate concerning 
the forms of life one would meet on Mars or Venus 
until we know something definite about what ele- 
ments and compounds occur in the atmosphere of 
these planets and in what proportions. Even small 
variations in the amount of carbon dioxide in the 
earth's atmosphere can seriously affect its climate. 
A slightly greater percentage of this compound in 
the atmosphere of Mars might go far toward over- 
coming the greater extremes of temperature be- 
tween day and night arising from a rarer atmos- 
phere and greater distance from the sun. 

Then, too, the relative amounts of nitrogen and 
oxygen in a planet's atmosphere would have to be 
taken into consideration in speculating on the pos- 
sibility of the existence of red-blooded organisms 
that require a large percentage of oxygen for their 
development. 

102 



SPLENDORS OF THE SKY 



The elements that enter into the composition of 
the earth's atmosphere and the percentage of these 
elements in a given volume are : Nitrogen, seventy- 
eight per cent. ; oxygen, twenty-one per cent. ; ar- 
gon, ninety-four hundredths of one per cent. There 
are, in addition, extremely small amounts of kryp- 
ton, helium, neon, xeon and other rare elements. 
The amount of water vapor in the air is, of 
course, variable wd can never exceed a certain 
amount, and the amount of carbon dioxide, as we 
stated before, is only three-hundredths of one per 
cent. 

There are in addition to these elements and com- 
pounds a number of impurities, such as ammonia, 
soot and dust particles that occur in extremely 
small amounts as a rule. We might also include the 
poisonous gases and compounds that man has em- 
ployed during the present war, though their sum 
total is infinitesimal and probably surpassed in 
total volume by the gases arising from a single 
volcanic eruption. 

The height of the earth's atmosphere can be de- 
termined by observing the flight of shooting stars 
or meteors and the altitude of the auroral stream- 
ers from two different positions on the earth's sur- 
103 



SPLENDORS OF THE SKY 



face, observations being made simultaneously at 
the two stations, or it can be determined from the 
duration of twilight. The results vary according 
to the method used, since the density of the atmos- 
phere decreases rapidly with increased distance 
from the earth and the different phenomena occur 
at different densities. 

The atmosphere extends fifty miles above the 
earth in quantities sufficient to produce twilight. 
It has been found that it is sufficiently dense to 
offer resistance to meteors at a height of 100 miles 
from the earth. The southern ends of auroral 
streamers are usually more than 100 miles in 
height; and they sometimes reach a height of 500 
miles. 

The aurora? are electrical phenomena of the rare 
upper atmosphere and the density required for 
their display is very slight. It is usually consid- 
ered that the atmosphere does not occur in ap- 
preciable amounts to more than 100 miles from the 
earth's surface. 

The weight of a column of air reaching from 

the earth's surface to the limits of the atmosphere 

and one square inch in cross section weighs fifteen 

pounds, and from the known area of the surface of 

104 



SPLENDORS OF THE SKY 



the earth it is possible to find the weight of the 
earth's atmosphere, which is approximately six 
quadrillion tons, or one-millionth of the mass of 
the earth. 



105 



CHAPTER XV 

HOW A LITTLE SPECTROSCOPE TELLS THE SECRET 
OF LIGHT 

IT IS rightly considered one of the greatest 
achievements of science that a tiny ray of light 
coming to lis from the immeasurable depths of 
space can be made to unfold the secrets of the com- 
position and nature of the body from which it 
emanates, whether it is gaseous or solid, highly 
heated or comparatively cool, new or far advanced 
in evolution, and even the amount and direction of 
its motion. 

The little instrument that accomplishes such 
wonderful results is known as the spectroscope and 
the field of study that it has opened to us is known 
as spectrum analysis. The essential part of the 
spectroscope is simply a glass prism, or chain of 
prisms in some eases, or it may be a piece of plane 
106 



SPLENDORS OF THE SKY 



glass or speculum, metal closely ruled with fine 
lines, sometimes as many as 20,000 lines to the inch, 
known as a diffraction grating. In each case the 
object is to separate white light into the various 
colors that enter into its composition. When a ray 
of white light such as sunlight is passed through a 
transparent medium denser than air, such as glass 
or water, it is split up into its component parts, 
which are rays of different colors and wave lengths. 
We have then what is known as the spectrum. This 
principle we have all seen illustrated in the rain- 
bow, which is formed when rays of white light or 
sunlight pass through falling drops of water, which 
act as tiny prisms and split white light into the 
rays of different wave lengths and color that com- 
pose it. All the colors of the rainbow are familiar 
to every one and they are the colors of the spec- 
trum. If, as in the spectroscope, a ray of sunlight 
is passed through a glass prism we see a ribbon of 
variegated colors blending into each other grad- 
ually. If the prism is so turned that the red will 
appear at our left hand we shall see in order from 
left to right — red, orange, yellow, green, blue, in- 
digo and violet, arranged according to their respec- 
tive wave lengths. The red rays have the greatest 

107 



SPLENDORS OF THE SKY 



wave length and are the least bent from their course 
and the violet are the shortest and so the most re- 
fracted. The wave lengths of the visible spectrum 
vary from .0008 millimeter for the red to .0004 for 
the violet. When we consider that .0001 millimeter 
is equivalent to 1-250,000 of an inch and that we 
can measure a displacement of this amount in the 
spectrum the wonderful accuracy of measurements 
by this method is apparent. 

Beyond the visible red rays we have the "infra 
red" rays and beyond the violet rays the "ultra 
violet' ' rays. The human eye is not sensitive to 
these colors, but their presence has been detected 
by photography, in the ease of the ultra violet rays, 
and by the heat produced by infra red rays, which 
are sometimes spoken of as "heat rays." The pho- 
tographic plate is particularly sensitive to the violet 
end of the spectrum. Very much can be accom- 
plished in spectrum analysis by means of the 
photographed spectrum. 

An examination of the spectrum produced by a 
ray of sunlight, which is known as the solar spec- 
trum, shows a great number of fine dark lines 
crossing the solar spectrum vertically. These are 
the absorption lines, sometimes called the Frauen- 
108 



SPLENDORS OF THE SKY 



hofer lines, and it is these dark lines that tell us 
so much of the temperature and constitution of 
the sun. 

Every chemical element when heated to vapori- 
zation and every gas heated to incandescence has 
its own characteristic spectrum, certain bright lines 
that essentially belong to it alone and that always 
appear in exactly the same position in the spec- 
trum. The greater the heat the more intense the 
lines appear, so the spectroscope can detect tem- 
perature changes. No two elements can have the 
same lines in the spectrum nor any lines in com- 
mon. "When a compound of sodium, for instance, is 
heated to vaporization, two lines characteristic of 
sodium appear in the yellow of the spectrum al- 
ways in exactly the same position. They are the 
characteristic lines of sodium, and if they appear 
in the spectrum of a certain star we know that 
sodium occurs in that star in a state of vaporiza- 
tion. If, however, a still hotter source of light is 
placed behind the vapor of sodium so as to shine 
through it the sodium lines appear as dark lines 
in the spectrum of the hotter light. Any other ele- 
ment, of course, acts in the same way when placed 
before a brighter light and the dark lines of the 
109 



SPLENDORS OF THE SKY 

substance are then spoken of as absorption lines. 
Take away the source of light beyond and they ap- 
pear as bright lines again. 

The dark lines that appear in the solar spectrum 
are the lines of vaporized elements that surround 
the hotter surface of the sun, and it has been 
through comparison of these lines with the bright 
lines produced by known terrestrial elements in the 
laboratory that we have found that the sun con- 
tains many elements that occur on the earth. It is 
an interesting fact that at the time of total solar 
eclipse, after the surface of the sun has been en- 
tirely hidden by the moon and before the surround- 
ing gaseous envelope has been covered, the dark 
lines of the solar spectrum suddenly flash forth as 
bright lines. This is what we should expect, for 
when the hotter source of light beyond is removed, 
the absorption lines appear as the bright lines of 
vaporized elements shining by their own light. 

There is a principle of spectrum analysis the 
value of which can hardly be overestimated in con- 
nection with the study of the heavens, for it has 
opened an entirely new field of discovery only 
secondary in importance to that opened up by the 
discovery of the telescope. That is, if a body emit- 
110 



SPLENDORS OF THE SKY 



ting light, such as a star or nebula, is in motion 
either toward us or from us, this motion will show 
in its spectrum. If the body approaches us the 
wave lengths of the ray of light entering the spec- 
troscope are of greater frequency and therefore 
shortened in length and all the lines of the spec- 
trum show a shifting toward the violet end of the 
spectrum, and if the body is receding from us the 
wave lengths are of less frequency and, so, longer 
and all lines are shifted toward the red end of the 
spectrum, and the amount of the shift measures 
the velocity of the motion. This fact enables us 
to confirm the time of rotation of different portions 
of the sun's disk formerly determined by means of 
sun spots. It also tells us that the stars are moving 
and that the motion of a star in the line of sight 
varies from a few miles a second to over 200 miles 
a second in extreme eases. It is not usual, how- 
ever, to find stellar motions greater than forty miles 
a second in the line of sight though the actual mo- 
tions may be considerably greater. It shows the 
great accuracy of these measurements that stellar 
motions as small as one-fifth of a mile a second can 
be detected. The surprising fact has been indi- 
cated by the spectroscope that the stars least 
111 



SPLENDORS OF THE SKY 



advanced in evolution move the most slowly, and as 
the age of the star increases the velocity increases. 
A star starts in the beginning with hardly any mo- 
tion and acquires increasing velocity. It is now 
generally believed that stars form in the regions of 
the Milky Way and as their velocity increases 
they move further and further away from this 
plane. 

We can no more than touch upon a few of the 
many wonderful truths revealed to us by the spec- 
troscope. Stars have been grouped into classes ac- 
cording to their spectra. There is the Orion type, 
often called the Helium type from the prominence 
of the lines of that element in the spectra of such 
stars. The Sirian type, named after its most prom- 
inent member, Sirius, shows hydrogen lines in great 
intensity. The Calcium type, named from charac- 
teristic lines of calcium, shows intense hydrogen 
lines as well. The Solar type, which includes our 
own sun, has its spectrum crossed by numerous 
dark metallic lines such as appear in the solar 
spectrum, and also hydrogen lines. In the type 
called K, which is next in evolution, the hydrogen 
lines have become fainter than some of the metallic 
lines. In the type last in evolution, composed of 
112 



SPLENDORS OF THE SKY 



dark reddish stars and known as type M, the spec- 
trum is characterized by fiutings due to titanium 
oxide. It is considered very remarkable that spec- 
tra of this type are so dominated by this one sub- 
stance. These types have been named in the gen- 
erally accepted order of evolution ; a star may pass 
in its life through all these different stages. 
Earlier than the Orion stars occur, however, stars 
of type 0, called Wolf-Rayet stars, whose spectra 
consist of bright bands on a faint, continuous back- 
ground. These latter stars are all found in the 
plane of the Milky Way and at great distances, 
and are believed to come first in evolution. The 
great Andromeda nebula shows a spectrum, in 
which most of the lines of this type are present. 

The Orion and Sirian stars, which come early 
in evolution, are blue-white and white stars. The 
solar type includes the yellow stars and the later 
types the reddish stars. 

In the study of our own sun, pressure, magnetism 
and radiation are all detected and measured by 
the spectroscope. Among double stars we are find- 
ing, by means of the spectroscope, an ever-increas- 
ing number that are so close together that they are 
beyond the reach of the most powerful telescopes, 

113 



SPLENDORS OF THE SKY 

but the shifting lines of the spectrum reveal the 
mutual revolution of the two components. 

In this modest little instrument we possess a key 
to many mysteries of the heavens that would other- 
wise be forever beyond our reach. It is little won- 
der that the astronomy of the spectroscope is called 
the "new astronomy' ' and by its means we hope to 
obtain an ever-increasing knowledge of the uni- 
verse. 



114 



CHAPTER XVI 

SECRETS OF THE SUN REVEALED BY THE SPECTROSCOPE 

TjRACTICALLY all that man knows of the phys- 
■■• ical constitution of our sun, which is simply- 
one of the stars, has been discovered through 
painstaking examination of several thousand fine 
dark lines in the solar spectrum, spoken of usually 
as the Frauenhofer lines. 

These investigations have been carried on in con- 
nection with extensive laboratory experiments with 
the spectra of all the known elements found upon 
our planet. 

Not only the nature and distribution of the ele- 
ments that exist in the sun's atmosphere have been 
determined in this way, but a number of very im- 
portant additional facts have been ascertained as 
well, such as the magnetic field existing in sun 
spots and the amount of pressure prevailing at 
115 



SPLENDORS OF THE SKY 



the sun's surface. All the various forms of solar 
activity are constantly being recorded in the lines 
of the solar spectrum and to interpret the evidence 
correctly is the duty of the astronomer engaged in 
solar research. 

The solar spectrum consists of a continuous band 
of variegated color crossed vertically by an enor- 
mous number of fine dark lines, fully 14,000 of 
which have been mapped and their wave lengths 
determined with a high degree of accuracy. 

It is, of course, the relative positions of these 
dark lines in the spectrum that are important and 
not the bright, continuous band of color upon which 
they arc projected, and which owes its origin to the 
intensely hot solar core of incandescent gases under 
high pressure. The dark lines originate in the 
cooler solar atmosphere lying just above the visible 
solar surface and are in reality not dark except by 
contrast. Remove the brilliant background and 
they appear as bright lines. This is exactly what 
occurs at the beginning of totality at the time of a 
total eclipse of the sun when they produce what is 
known as the " reversed " or flash spectrum. 

As the moon passes before the sun the solar sur- 
face is covered more and more until finally there 
116 



SPLENDORS OF THE SKY 



comes a moment when the last slender crescent of 
light disappears. The brilliant background has 
been removed and the portion of the solar atmos- 
phere lying just above the surface of the sun at 
the rim shines forth by its own light. The lines of 
the spectrum that are usually black on a bright 
background are now brilliant against a background 
that is black. This phenomenon is visible at the 
eastern edge of the sun at the beginning of totality 
and at the western edge at the end and is referred 
to as the flash spectrum. It lasts but a moment, 
as this lower solar envelope, spoken of as "the re- 
versing layer" since it reverses the solar spectrum 
at this time, is very shallow, and so is quickly cov- 
ered by the moon. 

It is possible to compute its depth from the 
known motion of the moon and the duration of 
flash spectrums and it is found to be about 500 
miles. In this layer occur the dense metallic va- 
pors that give the dark lines of the spectrum, which 
are called absorption lines because they ab- 
sorb from the light beyond exactly the same rays 
of which they themselves consist. Since to each 
chemical element belongs always the same definite 
group of lines in the spectrum, unvarying in posi- 
117 



SPLENDORS OF THE SKY, 

tion even under a wide range of temperature and 
pressure, it is possible to determine from the po- 
sitions of the various lines the elements to which 
they belong. By producing the spectra of all the 
familiar terrestrial elements in the laboratory, by 
heating them to incandescence in various ways and 
passing their light through the spectroscope, it has 
become possible to measure and map the lines of 
all known substances and to identify them as far 
as possible with the lines of the same elements 
found in the sun's spectrum. Since the light from 
the sun's interior gives the continuous band of 
color it is the gases that compose the sun's atmos- 
phere and not the sun's interior that are studied. 
Thirty-eight terrestrial elements are known to 
exist in the lower solar atmosphere. These are 
chiefly the metallic elements and hydrogen and 
helium. Carbon occurs only in compounds and free 
oxygen has been detected with great difficulty. 
Titanium oxide is found in abundance in sun spots. 
Some of the heavier elements, such as gold and 
mercury, are missing, but this may be due to the 
fact that the heavier elements probably lie at a 
greater solar depth and therefore do not appear in 
a spectrum belonging to the higher levels. 
118 



SPLENDORS OF THE SKY 



It is a peculiar fact that none of the " negative' ' 
elements appear in the solar spectrum. The halo- 
gen group, including such elements as chlorine and 
bromine, the oxygen group including the import- 
ant element sulphur and the nitrogen group are 
not to be found in the sun, though nitrogen appears 
in the form of cyanogen. The explanation has 
been offered that the spectrum of an element is 
sometimes entirely suppressed by a small amount 
of another element. The spectral lines of the non- 
metals are apt to be suppressed by the metallic 
elements. It is well-known that helium does not 
absorb the rays from the solar surface and does 
not give a dark absorption line, as in the case with 
all other known gases. This is in flat contra- 
diction to one of the fundamental laws of spec- 
trum analysis. This is simply another peculiarity 
of this very unusual gas. It occurs in abundance 
in the sun, however, and its characteristic bright 
yellow line is in the flash spectrum and can always 
be seen when the light of the photosphere is 
screened off. 

Of the fourteen thousand dark lines of the solar 
spectrum that have been mapped, one-third are 
"telluric" lines originating in our own atmosphere 
119 



SPLENDORS OF THE SKY 



and are due to absorption of the sun's rays by 
gases in the earth's atmosphere, chiefly oxygen, 
carbonic acid gas and water vapor. 

The origin of about six thousand of the solar 
lines is still undetermined or doubtful. Some of 
these are extremely faint. Of course, many of 
them may belong to a single element There is 
great disparity in the number of lines belonging to 
the various elements. The spectrum of iron is 
represented by more than two thousand lines in the 
solar spectrum, calcium by about seventy-five and 
lead by only one. The work of identifying the lines 
of the solar spectrum is still going on and it is ex- 
pected that all the doubtful and unknown lines 
will be traced to their origin before many years. 

Changes in solar temperature and pressure regis- 
ter their effect upon the appearance of the lines 
of the spectrum. Motion of the source of the light 
toward or from the observer, as motion of the west 
limb of the sun toward the earth and of the east 
limb in the opposite direction due to the rotation 
of the sun on its axis, causes a shift of all the spec- 
tral lines toward either the violet or the red end 
of the spectrum, according to a well known law of 
spectrum analysis. The periods of the sun's ro- 
120 



SPLENDORS OF THE SKY 



tation, varying according to latitude, have been 
accurately determined from this shifting of the 
dark lines of the spectrum. 

By special contrivance light can be reflected from 
the two limbs so that two spectra may be produced 
simultaneously, the one from one limb immediately 
above the one from the other. The effect of the 
sun's rotation can then be determined very accu- 
rately from the double displacement of the lines. 
The lines originating in the earth's atmosphere 
will not show this shift and can be readily identi- 
fied at this time. Increase of pressure in the solar 
atmosphere will broaden the lines and shift them 
all slightly toward the red. The continuous spec- 
trum that forms the background of the dark lines 
is due to the light coming from the sun's interior 
where the pressure is so great that the lines have 
probably been broadened until they coalesce. 

Dark absorption lines at times become tempor- 
arily bright in the centre for all or part of their 
length. This is spoken of as reversal of the lines, 
and is due to a hotter source of light suddenly 
being thrown in front of a cooler gas. This fre- 
quently occurs when some solar eruption causes a 
sudden upheaval of low lying, highly heated 
121 



SPLENDORS OF THE SKY 

It is often seen in the spectral lines of promi- 
nences. 

At times double reversals of lines are seen, par- 
ticularly of the sodium and magnesium lines. In 
such cases the bright line itself widens and a fine 
dark line appears in the centre. This appears to 
be due to large quantities of the vapor at great 
density. 

The dark lines of the spectrum often appear dis- 
placed and distorted, due to a sudden upheaval of 
gases and outbursts of solar activity in the vicinity 
of prominences. 

A most important effect frequently observed in 
the vicinity of sun spots is that known as the 
Zeeman effect. This is the splitting of a line into 
two or more components of opposite polarity, due 
to the presence of a magnetic field. It was from 
observing this effect that Hale discovered the mag- 
netic field existing in sun spots. There is a whirl- 
ing or vortical motion in sun spot regions carrying 
along electrically charged particles that produce 
the magnetic field. In fact, it has been found re- 
cently that the whole sun is in a magnetic field 
whose poles agree very closely with the sun's poles 
of rotation, and it is also possible that the earth 
122 



SPLENDORS OF THE SKY 



and sun may be in magnetic states as a result of 
their rotation and that all rotating bodies are 
magnetic. 

It has been possible to touch upon only a very 
few of the most important facts that have been 
discovered from careful study of the dark lines of 
the solar spectrum made with that most valuable 
instrument, the spectroscope. The branch of solar 
physics is probably the most fruitful of all fields 
of astronomical research, and our knowledge of 
the nature of the sun and its surroundings is in- 
creasing rapidly. 



123 



CHAPTER XVII 



THE SPOTS ON THE SUN 



SUN spots appear singly and in groups in con- 
stantly recurring cycles upon the surface of the 
sun. Near what is known as the period of sun 
spot maximum, the photosphere or visible solar sur- 
face is never clear. It is often possible at such a 
time to count as many as fifty spots occurring 
singly or in groups. Large single spots are less 
frequent than groups consisting of a fairly large 
spot accompanied by a train of smaller ones. Spots 
vary greatly in size. Isolated spots frequently at- 
tain a diameter five times that of the earth, and 
sun spot groups at times cover an area of more 
than one-tenth of the sun's diameter. 

The average duration of a sun spot is two or 
three months, though some last only a few days. 
They are carried across the solar disk from west 
124 



SPLENDORS OF THE SKY 



to east, and the average time it takes a spot to per- 
form a revolution is twenty-seven and one-fourth 
days. Different spots show considerable difference 
in time of rotation, as we should expect, for the 
sun's period of rotation is not constant as is the 
case with the earth, but varies greatly for different 
solar latitudes. Spots, moreover, have slight mo- 
tions of their own which affect their time of revo- 
lution. A spot is visible continuously for about 
two weeks, appearing at the western edge of the 
sun and disappearing over the eastern edge, to re- 
appear once more at the western limb after two 
weeks have elapsed, provided it has not suffered 
dissolution in the meantime. Spots often appear 
and reappear for several successive solar rotations 
with no marked change of form. 

At times a sun spot will form in a single day, 
again it will require days or even weeks for com- 
plete development. Usually there is disturbance of 
the solar surface for some time before the appear- 
ance of a spot. Many brilliant faculae, which are 
intensely bright flecks upon the sun's surface, 
make their appearances, and among these are scat- 
tered very small, black dots which gradually en- 
large. Between the black djots appear grayish 
125 



SPLENDORS OF THE SKY 



patches, which have the appearance of a veiled dark 
mass. This veil gradually fades away and we see 
the perfected spot. This consists of a dark central 
portion or umbra and an extensive grayish penum- 
bra. The black dots either coalesce with the prin- 
cipal spot or disappear or go to form an attendant 
train of smaller spots. 

When a spot is formed it is usually roughly cir- 
cular in form and remains without marked change 
until it breaks up. When this occurs the surround- 
ing solar surface seems to crowd in upon the pe- 
numbra and bridges of light that are often much 
brighter than the average solar surface span the 
umbra or dark central portions. The spot disap- 
pears as if overwhelmed and the disturbed surface 
is again covered with the brilliant flecks or faculae 
which are regions of intensely high temperature. 
Frequently the disturbance breaks forth anew at 
the same spot after a few days' interval and an- 
other spot may appear exactly where the old one 
disappeared. This appearance and disappearance 
may be repeated several times. Occasionally a 
large spot divides into two or more and the parts 
seem to repel each other and fly asunder with a 
velocity that may reach as high as a thousand miles 
126 




THE GREAT NEBULA IN ORION 

(Photographed by Ritchey with the 2-ft. reflector of the Yerkes Observatory) 



SPLENDORS OF THE SKY 



an hour. This repulsion probably arises from the 
fact that a strong magnetic field exists in sun spots, 
adjacent spots frequently being of opposite po- 
larity. 

When a sun spot is forming, eruptive promi- 
nences appear in the immediate neighborhood. 
These are upshooting jets of gases that attain a 
height of 20,000 or 30,000 miles on the average. 
They are varied and beautiful in appearance and 
change in form with great rapidity, often at a rate 
of 100 miles a second. 

Sun spots are confined to certain definite zones 
or belts upon the sun's surface. They are never 
found at the equator or poles. In fact, their ap- 
pearance beyond forty degrees north and south of 
the equator is extremely rare. They usually ap- 
pear between ten degrees and thirty degrees north 
and south latitudes, and in the long run appear as 
frequently in one hemisphere as the other. 

The periodicity of sun spots is one of the most in- 
teresting and most puzzling facts concerning them. 
Within a period whose average length is about 
eleven years, sun spots go through a cycle of maxi- 
mum and minimum appearance. At time of maxi- 
mum spottedness the sun's surface is never free 
127 



SPLENDORS OF THE SKY 



from spots; at the minimum weeks may pass with- 
out the appearance of a single spot. Although the 
average cycle is eleven years, individual periods 
may vary greatly, running from seven to seventeen 
years in duration. Attempts have been made to 
show that a larger period of thirty-three and one- 
third years exists, of which the smaller periods are 
subdivisions. When we know the cause of the sun 
spot cycle we shall have advanced far in the solu- 
tion of the mystery of sun spots and all their num- 
erous allied phenomena. 

Sun spot spectra have been extensively studied 
and much has been learned from this means of 
investigation. They show the presence of strong 
magnetic fields as well as a marked cooling of over- 
lying gases, and the presence within spots of such 
compounds as titanium oxide and calcium and 
magnesium hydride. These compounds could only 
form at comparatively low temperature and it is 
assumed that sun spots are regions of cooler solar 
temperature of about 3,500 degrees C, as com- 
pared with 6,000 degrees C. for the remainder of 
the photosphere. 

The presence of the compounds above mentioned 
gives the sun spot spectra their peculiar fluted ap- 
128 



SPLENDORS OF THE SKY 

pearance, which is also seen in the red type of 
stars. This is very significant when we consider 
that the red stars are the older and cooler stars. 
Are sun spots then one of the signs of the sun's 
advancing age f And will they increase in size and 
importance as the sun grows older? 

Sun spots, it is now believed, are manifestations 
of some deep-lying disturbance that is of far-reach- 
ing importance. Many phenomena go through 
cycles of change in keeping with the sun spot cycle. 
Among these are magnetic storms and magnetic 
disturbances upon the earth which are closely de- 
pendent upon the sun spot period. Severe mag- 
netic storms upon the earth occur at a time when 
the sun's face is strongly spotted, and displays of 
northern and southern lights are also most marked 
at this time. The general surface air temperature 
of the earth is lower by about a degree at the time 
of maximum spottedness of the sun. 

One of the most marked effects of the sun spot 
cycle is the form of the solar corona, which is only 
visible at time of total solar eclipse. At the time 
of a maximum sun spot period the corona is an 
evenly developed halo surrounding the sun. At 
the sun spot minimum it shows equatorial stream- 

129 



SPLENDORS OF THE SKY 

ers that often extend to a distance of several times 
the sun's diameter, while on either side of the 
solar poles only short filaments of light appear. 
So decided are these changes in the form of the 
corona with the change in the sun spot period that 
the two types are spoken of as "the sun spot max- 
imum corona" and "the sun spot minimum co- 
rona." 

As to what causes these periodic outbreaks upon 
the solar surface we are still in the dark. Some 
astronomers believe they are caused by external 
influences such as periodic returns of swarms of 
meteors or returns of certain planetary configura- 
tions. Careful and long-continued observations 
seem to show that sun spots are rather the result of 
internal disturbances which cause a transference of 
solar matter from within outward in a cyclonic mo- 
tion, which has been compared in form to that of 
whirling waterspouts at sea. The central stem 
forms the umbra and the outspreading gases the 
penumbra. There is a tendency for a vacuum to 
form in the centre of the whirl and into this is 
drawn the overlying gases, chiefly hydrogen. 

The rapid expansion of gases as they approach 
the solar surface from within causes a sudden cool- 
130 



SPLENDORS OF THE SKY 



ing, which accounts for the comparatively low 
temperature in spots and the formation of such 
solids as titanium oxide and the hydrides of cal- 
cium and magnesium. These dissimilar substances, 
it is believed, give rise by friction to the magnetic 
field which is known to be a feature of sun spots. 

It is hoped that continued solar research will 
make known in time the cause of these peculiar 
periodic disturbances that are so far reaching in 
their effect. 



131 



CHAPTER XVIII 



SOLAR EXPLOSIONS 



\ MOST interesting discovery has been made 
*■*■ within the past few years of the sudden, but 
rather infrequent, appearance at the surface of 
the sun of hydrogen "bombs," as they have been 
called. 

These "bombs" are apparently violent explo- 
sions of highly heated hydrogen gas in regions of 
great solar activity. At times, according to Dr. 
Ellerman, of the Mount Wilson Observatory, 
who discovered them, they will follow one another 
like balls of a Roman candle at intervals of ten or 
twenty minutes. The duration of the explosion is 
usually about two or three minutes, more rarely 
five or ten minutes. The "bombs" generally ap- 
pear on the edge or at one side of active sun spot 
groups that are developing and are composed of 
132 



SPLENDORS OF THE SKY 

many members. Repeated explosions often occur 
almost exactly in the same place. 

The presence of the "bombs" is revealed by the 
appearance of two intensely brilliant narrow bands 
of nearly uniform width on either side of the dark 
absorption line of hydrogen that is associated with 
the higher solar atmosphere. The fact that the 
dark line itself is not interfered with nor any 
other of the absorption lines belonging to the va- 
rious strata of the sun's atmosphere shows that 
the explosions occur considerably below the chro- 
mosphere, the lowest, densest layer of the solar 
envelopes, in which are to be found the majority 
of all the gaseous elements that compose the sun's 
atmosphere. 

The area covered by the explosion is so small 
that the bombs can only be seen with a large solar 
image and under fine "seeing" condition. Dr. 
Ellerman first saw the two brilliant bands sud- 
denly appear one on each side of the dark absorp- 
tion line of hydrogen in September, 1915, while he 
was observing the dark line for distortions and 
reversals in connection with an active sun spot 
group. 

Within two minutes the bright bands disap- 
133 



SPLENDORS VF THE r SKY 



peared and were not seen again. A month later 
additional explosions were recorded visually and 
photographically. 

The phenomenon of the solar hydrogen " bombs' * 
has now been recognized for some time as an estab- 
lished feature of solar activity. The close associa- 
tion of hydrogen with sun spots in the form of 
vast eruptive prominences of highly heated hydro- 
gen and the descent of cooler hydrogen from the 
upper solar atmosphere into the vortices of sun 
spots has long been known. 

A most valuable instrument employed in study- 
ing the distribution of the various gases in the 
sun's atmosphere is the spectroheliograph, which is 
simply a moving spectroscope timed to travel over 
the •solar disk at a uniform rate with the slit of the 
instrument so adjusted that the light from only 
one line of an element in the solar spectrum is ad- 
mitted to the eye or the photographic plate. 

In this way the distribution of the vapors of in- 
candescent hydrogen or calcium, iron or any other 
element at different levels of the sun's atmosphere 
can be studied in great detail as well as the con- 
nection of these elements with sun spots and other 
solar phenomena. When the sun is viewed witli 
134 



SPLENDORS OF THE SKY 



the spectroheliograph in the light of a single spec- 
tral line of hydrogen it is possible to detect the 
presence of the flames of incandescent hydrogen in 
the prominences by their projection on the sun's 
disk as irregular dark patches or streaks as well as 
to study their infinite variety of forms when the 
slit of the instrument is set at the edge of the sun's 
disk. 

When the surface of the sun is viewed telescopic- 
ally, it presents a peculiar mottled appearance, or 
rice-grained structure, as it is called. The spec- 
troheliograph shows that this same structure is 
found in the chromosphere and in the higher solar 
atmosphere. The rice grains of the sun's surface 
are intensely brilliant flecks of light, each com- 
posed of a great number of minute granules or 
mere points of light. 

The rice grains are usually about 400 miles in 
diameter, while the granules measure less than ten 
miles across. In sun spots these minute granules 
are replaced by minute filaments that group them- 
selves into the familiar " thatch straw" structure 
of the penumbra that surrounds the umbra or dark 
central portion of sun spots. 

It is now believed that the granules and the fila- 
135 



SPLENDORS OF THE SKY 



ments are all the same. Columns of highly heated 
gases arise by convection from the sun's interior. 
The granules are cross section views of these ver- 
tical columns. In the vicinity of sun spots the 
ascending columns of gases are drawn into posi- 
tions more or less at right angles to their normal 
positions by the whirling vortical motion existing 
in sun spot regions, and they then appear as the 
long, slender filaments that form the thatch straw 
structure of the penumbra of sun spots. 

Now the spectroheliograph shows in the layers 
of the sun's atmosphere above the photosphere the 
same peculiar structure. The "flocculi" of hydro- 
gen and calcium resemble in appearance the rice 
grains of the sun's surface. These flocculi are 
ascending columns of expanding and cooling hy- 
drogen and calcium vapors that rise far above the 
level of the photosphere, or visible surface of the 
sun. 

It is an interesting fact that different spectral 
lines of an element usually are associated with dif- 
ferent levels of the sun 's atmosphere. The element 
hydrogen, for instance, has lines in the red end of 
the spectrum and lines in the violet. The red rays 
of any element in the sun rise normally to a much 
136 



SPLENDORS OF THE SKY 



higher level than the violet rays, for the rays of 
shortest wave length, violet and ultra-violet rays 
are more liable to be trapped in the denser lower 
atmosphere of the sun, while the longer red rays 
escape. 

By setting the spectroheJ.iograph on the violet 
lines of hydrogen the distribution of hydrogen in 
the lower levels can be studied, and by setting on 
the hydrogen lines in the red the scarlet names of 
incandescent hydrogen gas in the prominences that 
reach to heights of 100,000 or 200,000 miles above 
the photosphere can be exhaustively examined. 

It is possible that there are rays of extremely 
short wave length in the sun's interior that never 
reach the photosphere, but are imprisoned far be- 
neath, while the red, orange and green rays of the 
various elements escape readily to the surface and 
the higher atmosphere of the sun. As a result the 
sun presents a decidedly yellowish hue to the eye. 

The calcium flocculi representing highly heated 
columns of calcium gas are bright flecks on a dark 
background, for they are at a higher temperature 
than the surrounding gases, which appear dark by 
contrast, but still higher up, where hydrogen alone 
persists, the hydrogen flocculi appear dark against 
137 



SPLENDORS OF THE SKY 



a bright background of diffused gases, for at the 
reduced temperature of the higher level the ex- 
panded and cooled hydrogen shows its presence by 
absorption. 

Photographs of these upper regions taken with 
the slit of the spectroscope set on the hydrogen line 
characteristic of this elevation show most interest- 
ingly the peculiar distribution of hydrogen gas 
here. Irregular dark streaks projected upon the 
sun's disk show the presence of eruptive or quies- 
cent prominences. Above sun spots or sun spot 
groups the hydrogen flocculi are curved either in 
clockwise or counter-clockwise direction, showing 
that a whirling motion of the hydrogen gas exists 
and that it is being sucked downward with a cy- 
clonic motion into the umbra? of the sun spots that 
lie at the level of the solar surface. 

The revelations of the spectroheliograph are, 
therefore, rich in information concerning the dis- 
tribution and behavior of the gases that are found 
at the surface of the sun and in all the different 
layers of its atmosphere. 

It pictures a sun of explosions, eruptions and 
ceaseless activity. Countless columns of highly 
heated gases of many elements rise to the surface 
138 



SPLENDORS OF THE SKY 



and penetrate in some instances even into the 
higher solar atmosphere, the lightest elements at- 
taining the greatest heights, later to descend in 
cooler streams or cyclonic whirls to the photosphere 
and the sun spot regions. 



139 



CHAPTER XIX 

SOME RECENT TOTAL SOLAR ECLIPSES AND THEIR VALUE 
TO ASTRONOMY 

T^CLIPSES as well as comets were always hailed 
■" in ancient times with dire misgivings, and 
even at the present day the uneducated and 
ignorant of all lands are not entirely free from 
fear and superstition regarding these celestial hap- 
penings. Up to a few centuries ago it was firmly 
believed that such phenomena heralded some 
ominous change and there are instances in history 
of abandonment of certain enterprises and even 
cessation' of battles and a peace hastily concluded 
due to the sudden darkening of the sun's face. 
In modern times, on the contrary, we find scientists 
bending every effort to observe all total eclipses 
of the sun in whatever portion of the world they 
may chance to fall that they may extend their 
140 



SPLENDORS OF THE SKY 



knowledge of the wonderful physical constitution 
of our sun and its mysterious coronal halo. To 
obtain observations during a few fleeting moments 
many hardships have been undergone by eclipse 
expeditions. Many disappointments have also 
been experienced in connection with this work. 

The French astronomer Janssen escaped from 
Paris in a balloon at the time of the siege of Paris 
in 1870, carrying the essential parts of his instru- 
ments with him for the purpose of observing the 
total eclipse of the sun visible that year in Spain 
and Africa, only to be defeated by clouds. 

"War as well as clouds has been the enemy of 
many an eclipse expedition. At the beginning of 
1914 elaborate plans were well advanced in many 
lands for observation of the total eclipse of Aug. 21, 
1914, visible in Europe from Norway and Sweden 
through Russia to Persia, with a duration of about 
two minutes. All the leading countries of Europe, 
Argentina and the United States sent eclipse ex- 
peditions to Russia in the neighborhood of Riga 
and Kiev. Many expeditions were in the field set- 
ting up complicated photographic and spectro- 
scopic outfits and practising preliminary drills that 
all might go smoothly during the critical moments, 
141 



SPLENDORS OF THE SKY 



even as the armies of Europe were mobilizing for 
the greatest war in the history of the world. A 
few parties were successful in spite of war and 
generally prevailing clouds, but the majority were 
either turned back before reaching their destina- 
tion or experienced extreme difficulty in returning 
to their homes. Several German observers were 
detained as prisoners of war in Russia. The Lick 
Observatory expedition was compelled to return by 
way of Moscow, Finland and Sweden instead of by 
way of Berlin and Paris, as was originally planned, 
while their instruments were kept in Eussia for 
nearly four years. 

The first American eclipse expedition ever 
formed was sent to Penobscot in the War of the 
American Eevolution. The first total eclipse to be 
observed scientifically to any extent in North 
America was the eclipse of July 18, 1860. Three 
American observers, including Prof. Simon New- 
comb, the noted American astronomer, penetrated 
to the banks of the Saskatchewan to observe this 
eclipse, while the astronomer, Gilliss traveled to 
Washington Territory by way of Panama for the 
same purpose, and was amply rewarded by ex- 
cellent views of the solar prominences and the 
142 



SPLENDORS OF THE SKY 



corona. Another American expedition sent to 
Labrador was defeated by clouds. From that date 
to the present time American eclipse expeditions 
have been sent to the path of totality of every 
important solar eclipse, whether in Europe, Asia, 
Africa or South America. 

The eclipse of the 8th of June, 1918, was a 
return of the total eclipse of May 28, 1900, so suc- 
cessfully observed by a large number of eclipse 
expeditions in the Southern States from New 
Orleans to Norfolk. After an interval of eighteen 
years, eleven and one-third days, which is spoken 
of as the eclipse Saros, the earth, sun and moon 
returned to practically the same relative positions 
in the heavens and all the circumstances of the 
previous eclipse are repeated except for the 
fact that the fraction of a day in the period 
causes the eclipse to fall 120 degrees westward of 
its former position, the amount of the earth's rota- 
tion on its axis in this interval of time. In conse- 
quence a different portion of the earth's surface is 
visited by each returning eclipse of a given series. 
The eclipse of May 17, 1882, lasting only one minute 
and a half, but observed with great success by 
many eclipse expeditions in Egypt on the banks 

143 



SPLENDORS OF THE SKY 



of the Nile, belongs to this same eclipse family. 
The next return of the eclipse of June 8 will fall 
upon June 19, 1936, and its path will extend from 
the Mediterranean through southern Eussia and 
Asia to the Pacific coast. 

Since the path of totality of the eclipse of June 8, 
1918, passed diagonally across the United States 
from Washington to Florida, eclipse expeditions 
were sent to the central line from nearly all the 
leading observatories in the country. No foreign 
expeditions were in the field on account of the war 
and many American astronomers were unable to 
observe the eclipse for the same reason. 

Since it has now become possible to study the 
solar prominences without the aid of total eclipses 
and since the search for intra-mercurial planets 
appears to yield negative results, scientific interest 
has centred of late years chiefly upon the elusive 
coronal light, its nature and its cause and the 
character of the peculiar unknown gas coronium 
of which it is largely composed. Much is to be 
expected from future investigations along this line, 
but progress is necessarily slow, for so faint is 
the coronal light that the least percentage of direct 
sunlight completely masks it. So it is only when 
144 



SPLENDORS OF THE SKY 



the friendly moon interposes between the earth 
and sun and completely hides the solar surface 
that the beautiful pearly radiance of the corona 
may be seen. 

According to the reports of astronomers who 
observed the eclipse highly satisfactory results were 
obtained by many of the eclipse parties stationed 
between Washington and Kansas despite the fact 
that clouds gathered all along the path of totality 
within the United States. The success of the ma- 
jority of the expeditions is to be attributed to 
breaks in the overhanging clouds occurring just at 
the critical time. 

According to the report of Prof. W. W. Camp- 
bell, director of the Lick Observatory, who was in 
charge of the Crocker eclipse expedition at Golden- 
dale, Wash., observers at this station were pre- 
paring to accept complete defeat from dense clouds 
that overspread the sky from midnight of June 7 
to past midnight of June 8, when within less than 
one minute of total eclipse a sudden break in the 
clouds uncovered an intensely blue strip of sky 
and the thin solar crescent. The entire eclipse 
programme was most unexpectedly carried out with 
complete success. 

145 



SPLENDORS OF THE SKY 



Less than one minute after the end of totality- 
clouds once more covered the scene of the phe- 
nomenon. The "seeing" at the critical time was 
magnificent and the expedition became almost by a 
miracle the most successful expedition ever sent 
out from the Lick Observatory. 

Twenty-six excellent photographs of the corona 
were taken at Goldendale, ten with the forty-foot 
camera on a large scale and eight each with a 
forty-eight-inch coronal camera of three-inch aper- 
ture and an eleven-inch coronal camera designed 
for landscape work. The last two cameras were 
suitable for showing the general outline and form 
of the corona and the extent of the streamers. The 
longest coronal streamers recorded at Goldendale 
were approximately three solar diameters, or two 
and one-half million miles, in length. 

Six spectroscopic instruments mounted on a 
single polar axis registered valuable spectra of the 
corona and prominences, as well as of the chromo- 
sphere or lower solar atmosphere. 

The corona was particularly beautiful in form, 

belonging to the variety known as a "petal-formed" 

corona, a type occasionally noted in past eclipses. 

The "petals" are the result of rifts in the coronal 

146 



SPLENDORS OF THE SKY 



streamers and the crossing of curved rays. Seven 
distinct petals were noted in the June eclipse. 

Many observers described the corona as unusu- 
ally brilliant and of an intense blue-white color. 
In shape it was roughly triangular, the long 
streamers to the east of the sun forming the apex 
and the more evenly distributed streamers to the 
west the base of the triangle. 

The spectrum of the inner corona was ' ' continu- 
ous, ' ' that is a continuous band of variegated color 
with no dark absorption lines, showing that It 
shone by its own inherent light and not by re- 
flected sunlight. The outlying portions of the 
corona showed the faint absorption lines of the 
solar atmosphere and therefore it was evident that 
part of its brightness was due to reflected light 
from the sun. 

At least five unidentified bright lines were found 
in the coronal spectrum and their wave-lengths 
were measured, while the existence of seven other 
bright coronal lines was suspected. The nature of 
the element or elements connected with these lines 
is undetermined, though several of the lines doubt- 
less belong to the unknown element coronium. 

The wave-length of the characteristic green line 
147 



SPLENDORS OF THE SKY 



of coronium was accurately measured from spec- 
troscopic observations obtained during this eclipse, 
which will aid greatly in its future identification. 

The chromosphere, appearing as an extremely 
narrow orange-colored rim of light surrounding the 
sun and composed of incandescent gases of many 
metallic elements, contrasted beautifully with the 
pearly light of the corona tinged with the green 
rays of the unknown coronium whose nature as- 
tronomers are most anxious to discover from ob- 
servations obtained during total eclipses of the sun. 

Rising from the chromosphere are usually seen 
during totality a number of ' ' prominences, ' ' up- 
shooting flames of incandescent hydrogen gas of a 
deep scarlet hue. These outbursts of incandescent 
gases from the dense lower strata of the solar at- 
mosphere are at times very conspicuous and add 
to the weird beauty of this unusual scene. 

Even to the unaided eye the prominences of 
June 8, 1918, were a most beautiful feature of 
totality. Three huge blood red prominences, vary- 
ing from 45,000 to 60,000 miles in height, were 
visible 120 degrees apart. Though they were not 
higher than the average, their structure was ex- 
tremely interesting. One of these on the west edge 
148 



SPLENDORS OF THE SKY 



of the sun was likened to the skeleton of some 
prehistoric monster. A number of other minor 
prominences were visible, and the north and south 
poles of the sun chanced to be marked by two 
bright prominences. 

Several of the prominences were capped in a 
most peculiar manner by curved coronal rays re- 
sembling Gothic arches. The apexes of several of 
these arches lay at a distance of fully 200,000 miles 
above the solar surface. There appeared to be 
some connection between the coronal arches and 
the prominences. Doubtless the same force that 
caused the upheaval of the gases composing the 
prominences also produced the peculiar coronal 
caps above them. 

The coloring of the solar surroundings during 
totality of the June eclipse has been described by 
those who were privileged to observe it as gorgeous 
beyond description. The deep orange tinge of the 
chromosphere, contrasting with the intensely bril- 
liant blue-white light of the coronal rays curved 
into beautiful petal-like formations, and the huge 
blood red prominences presented a weird effect 
never to be forgotten. 

The great value of the next total solar eclipse, 
149 



SPLENDORS OF THE SKY 



that of May 29, 1919, lay both in its extraordinary 
duration, amounting to nearly seven minutes at 
maximum and far exceeding the average totality of 
three minutes, and also in the fact that the eclipsed 
sun was to be in a field particularly rich in stars, 
midway between the Hyades and the Pleiades, a 
position unusually favorable for testing the new 
theories bearing on the nature of light and the 
influence of the sun's gravitational and magnetic 
field upon the path of a ray of light. 

The belt of totality in this eclipse started on 
the western coast of South America, the boundary 
between Chile and Peru falling nearly on the cen- 
tral line, and the northern limit of totality passing 
only a few miles south of the Harvard College 
observatory station at Arequipa, Peru. 

Here the sun rose partially eclipsed, so it was 
not expected that valuable observations would be 
obtained with the sun so close to the horizon. 
Passing over the towns of La Paz and Trinidad in 
Bolivia, the path of totality entered Brazil, crossed 
to the Atlantic Ocean at a point about three de- 
grees south of the equator, passing almost centrally 
over the towns of Caxias and Sobral, where the 
duration was to be over five minutes, and then 
150 



SPLENDORS OF THE SKY 



crossed the Atlantic Ocean to Cape Palmas, Liberia. 

At St. Paul's Rocks in mid- Atlantic, at latitude 
one degree north and longitude thirty degrees west, 
the total phase was to last more than six minutes. 
Bending southward from Liberia the path of total 
eclipse passed over He Principe, or Prince 's Island, 
in the Gulf of Guinea, and Libreville in the French 
Congo; thence across the African continent to the 
Indian Ocean, the sun setting partially eclipsed 
over the island of Madagascar. 

British astronomers organized two eclipse expe- 
ditions to observe this eclipse. Both expeditions 
were equipped at the Royal Observatory at Green- 
wich and left England about the middle of March, 
one under Astronomers Crommelin and Davidson 
for Sobral in northern Brazil, and the other, under 
Prof. Eddington and Mr. Cottingham, for He Prin- 
cipe in the Gulf of Guinea. At both stations the 
total phase of the eclipse was to last more than five 
minutes, and it was the plan of the observers to 
concentrate all their efforts on testing the new 
theories of light and the effect of gravitation upon 
the course of a ray of light. 

The Bureau of Terrestrial Magnetism of the 
Carnegie Institute, under the directorship of 
151 



SPLENDORS OF THE SKY 



Dr. L. A. Bauer, made extensive plans for mag- 
netic and other allied observations of this eclipse. 
Dr. Bauer left for England early in March, where 
he organized an expedition to be stationed either 
at He Principe or Libreville in the French Congo. 
From there he proceeded to South America to 
arrange for similar observations near Sobral, as 
well as at a number of stations outside the belt of 
totality. Various magnetic observatories, institu- 
tions and individuals offered their co-operation for 
this purpose. 

Dr. C. G. Abbot, director of the astrophysical 
observatory of the Smithsonian Institution, left 
Washington the first of May for South America 
to observe the eclipse near Sobral, which was the 
chief station for observations on this continent. 
The eclipse was to occur in the early morning at 
this point, mid-totality coming shortly after 9 
o'clock, while at Libreville, in the French Congo, 
totality was to occur shortly before 3 o'clock in 
the afternoon, local time. 

The problem that the observers of this eclipse 

were anxious to solve is whether or not light obeys 

the laws of gravitation and is deflected from its 

course upon entering the field of the sun's attrac- 

152 



SPLENDORS OF THE SKY 



tion. Prof. Eddington, who was to observe the 
eclipse in the French Congo, characterized it as the 
problem of "weighing light/ ' 

According to the most recent theories light can 
no longer be regarded as an elastic wave motion 
of the universal ether that has been assumed to 
pervade all space, but rather as consisting of widely- 
separated centres of energy whose particles vibrate 
singly. 

It is known that light exerts pressure and has 
a finite velocity of 186,000 miles per second, and 
therefore it is reasonable to assume that it pos- 
sesses mass, momentum and, in the vicinity of a 
strongly attractive body such as the sun, appre- 
ciable weight, provided it obeys the laws of gravi- 
tation. It was, therefore, to see if light is com- 
posed of material particles obeying the Newtonian 
law of gravitation that this eclipse was to be ob- 
served. 

It is possible to determine just how far particles 
of matter coming from infinite space, in this in- 
stance rays of light from distant stars moving with 
a velocity of 186,000 miles per second, will be de- 
flected from their course upon entering the field 
of the sun's attraction, just as one can trace the 
153 



SPLENDORS OF THE SKY 



path of a comet or meteor under the same con- 
ditions. 

It can be shown that the path of any such par- 
ticle will have the form of a hyperbola con- 
cave toward the sun and that the nearer the par- 
ticles or light rays come to the sun's edge the 
greater will be the curvature of the paths and the 
greater the apparent displacement of the stars 
away from the sun. For a ray of star light just 
grazing the edge of the sun it has been found that 
a displacement of nearly one second of arc in the 
star's position is to be looked for if light obeys 
the law of gravitation. This would be the greatest 
displacement, for the nearer the rays pass to the 
sun the more strongly they are attracted and the 
more they are deflected from their course. 

Obviously stars near the sun are invisible ordi- 
narily. It is only during a total eclipse of the sun 
when the stars shine forth as on a moonlight night 
that it becomes possible to " weigh light" from 
observations of the stars in the vicinity of the sun. 

During this eclipse, it was expected at least thir- 
teen stars would be visible close to the sun's posi- 
tion. If displacements in the normal positions of 
all of these stars were observed and if the displace- 
154 



SPLENDORS OF THE SKY 



ments were greater the nearer the star came to the 
sun by the amount required by the theory it would 
be strong evidence in favor of the new theory that 
light possesses mass and weight and obeys the law 
of gravitation. 

The uncertainties attending observations of such 
a nature are necessarily great. Aside from uncer- 
tainties as to weather conditions there is the pos- 
sibility that the solar corona might affect the star 
positions, possibly refracting or blurring the images 
of the stars and thereby introducing errors in the 
measurements, 

Errors of instruments must also be reduced to a 
minimum to make possible accurate measurements 
of these angles of displacement that, if existent, 
scarcely exceed the parallaxes of the nearest stars. 

The expeditions fitted at the Royal Observatory 
of England expected to use the astrographic tele- 
scope employed for cataloguing the positions of 
the stars by photography, and it planned to make 
the exposures of the photographic plates of ten 
seconds duration. Comparisons of the positions of 
the thirteen stars obtained during the eclipse with 
the normal positions of these stars obtained when 
the sun is in another part of the heavens should 

155 



SPLENDORS OF THE SKY 



show the displacement due to the sun's influence 
on the path of a ray of light, if it exists. 

It is also possible to test at the same time the 
noted Einstein theory of relativity that is the 
subject of so much discussion at the present time. 
According to this theory the velocity of light is 
less in a strong gravitational field than it is in a 
vacuum, and the displacement of the light from the 
stars that passed through the field of the sun's influ- 
ence comes out twice that indicated by the first 
theory. 

It was difficult to obtain any information bear- 
ing on these problems of light and gravitation 
during the United States eclipse of June 8, 1918, 
owing to the fact that the sun was at that time in 
a field of very few stars. 

The results of the observations of this eclipse are 
not yet available but it is hoped that some of the 
expeditions were successful in obtaining photo- 
graphs that will be of value in solving this unique 
problem of weighing light. 



156 



CHAPTER XX 

ARE THERE OTHER PLANET WORLDS? 

T F IT were possible for man to view the solar sys- 
■*■ tern from the distance of the nearest star, our 
glorious orb of day would appear as a first magni- 
tude star, very similar to beautiful Capella, the 
star of yellow hue that shines so conspicuously 
near the meridian in northern skies in the early 
evening hours of February. 

If our greatest telescopes could be turned upon 
the sun at this distance, the existence of his planet 
family would never be suspected. Jupiter, the 
greatest of the satellites, would be a star of the 
twenty-first magnitude, shining by reflected light 
only and situated but five seconds of arc distant 
from the sun. When we consider that the most 
powerful telescope in existence cannot show stars 
below the twenty-first magnitude, even under the 

157 



SPLENDORS OF THE SKY 



most favorable circumstances, the impossibility of 
detecting even the greatest of the sun's family at 
this distance is clearly evident. 

The least distance that the unaided eye is able 
to distinguish between two stellar objects is more 
than 200 seconds of arc, so even if Jupiter shone 
with a lustre equal to that of the sun the two would 
appear as one star to the naked eye at the distance 
of the nearest star. As to the other planets: be- 
fore the bounds of the solar system are passed, 
Mercury, Venus, Earth and Mars sink into invisi- 
bility, mere cosmic specks lost in the rays of a sun 
that is rapidly assuming a starlike appearance 
even at this distance. 

We have likened the aspect of our sun at the dis- 
tance of the nearest star, that is, at a distance of 
only four light years, to the brilliant Capella, and 
spoken of the total invisibility of its greatest satel- 
lite, the mighty Jupiter, at this distance. How 
would our glorious sun appear if it were situated 
at the same distance from us as this conspicuous 
star of winter skies forty light years away? 

Instead of a brilliant first magnitude star we 
would barely see an insignificant point of light of 
the fifth magnitude, one-seventieth as bright as 
158 



SPLENDORS OF THE SKY 



Capella and near the limit of visibility for the un- 
aided eye. And yet Capella is not very far away 
as star distances go in a sidereal universe some 
300,000 light years in extent. Ten thousand light 
years away great telescopes could not pick up the 
tiny speck of light representing our sun among 
the innumerable hosts of the universe. 

The inconceivably great distances separating the 
various suns that compose our universe render ab- 
solutely hopeless any attempt to investigate the 
planet families of other suns, if such exist, and we 
very reasonably suspect that other planet worlds 
do exist. 

There are many stars in the stellar system that 
closely resemble our own. So the spectroscope tells 
us. Our sun is but one of the yellow stars. Line 
by line its spectrum is reproduced in many a star 
that is evidently composed of the same elements at 
practically the same stage of stellar evolution. If 
one member of this group is, to our knowledge, at- 
tended by a planet family, we can hardly assume 
that the reverse is true of all other stars of the 
same type. Inability to detect the presence of 
such worlds does not disprove their existence. 

Possibly the day may come when some device at 
159 



SPLENDORS OF THE SKY 



present unknown, as the spectroscope was less than 
one hundred years ago, may accomplish as wonder- 
ful results in the detection of dark bodies in the 
universe, whether sun-like or planetary in size, as 
the spectroscope has in the detection of dark and 
light suns physically associated in double or mul- 
tiple systems. 

It is the spectroscope that tells us that beautiful 
Capella is not a single star, such as our own sun, 
but belongs to a star system composed of two bright 
stars, each approximately equal in mass to our own 
sun, that revolve around a common centre of grav- 
ity in about one hundred days and are separated 
from each other by a distance of about fifty million 
miles. 

It is now well known that a large proportion of 
the stars are not single suns, but belong to systems 
of two, three or more suns in revolution around a 
common centre of gravity. The spectroscope tells 
us that some of these bodies are dark. They make 
known their presence only by the disturbance they 
produce in the motion of the bright stars with 
which they are associated. The fact that they can 
produce such disturbances proves that they are of 
sun-like dimensions and not planets. They are 
160 



SPLENDORS OF THE SKY 



dark either because they are extinct through old 
age or because they are, for some mysterious rea- 
son, imperfect radiators of light. 

A satellite such as Jupiter that possesses only 
about one-thousandth of the mass of the sun it en- 
circles could never appreciably affect the motion 
of its ruler. The spectroscope would not reveal the 
presence of such a modest attendant, though it 
possesses more than 300 times the mass and 1,300 
times the volume of our planet Earth. Yet small 
planetary bodies may, for all we know, be members 
of double and multiple star systems. There may 
be all gradations in such systems from dark bodies 
of sun-like mass, capable of revealing their pres- 
ence to observers hundreds or even thousands of 
light years distant, down to hopelessly obscure 
planets or planetoids such as our ringed Saturn, 
mighty Jupiter, modest planet Earth, or the num- 
berless asteroids of the sun's family. The masses 
of celestial bodies can only be found through their 
attraction for other bodies. It is impossible to 
know anything definite about the masses of solitary 
stars since they lie so far apart. 

Systems of connected stars, on the other hand, 
through the attraction of the various members for 

161 



SPLENDORS OF THE SKY 



each other, furnish a method for determining the 
combined masses of the stars in terms of our sun's 
mass when their distance from the earth is known. 
One of the interesting results of the investigations 
of the masses of these binary systems is to show that 
our sun is an average star. Though there are 
giants in the universe such as Arcturus or Cano- 
pus or Rigel that dwarf our sun into insignificance, 
and though nearly all the stars visible to the naked 
eye are far more brilliant than our luminary, they 
represent the exceptional stars. Among the tele- 
scopic stars, the countless hosts that go to form the 
sidereal universe, our sun is about the average in 
size and importance and in no respect remarkable 
unless we assume that, for some mysterious reason, 
the rays of this one alone are capable of fostering 
varied and multiple forms of life upon attendant 
planets. 

Binary star systems often present strange and 
unexplained variations of light. In some instances 
light variations are due to the temporary eclipse of 
one member of the system by the other, as in the 
noted Algol system. There are, on the other hand, 
light changes in other binary stars not so easily 
explainable. The Cepheid variables, as they are 
162 



SPLENDORS OF THE SKY 



called, have so far defied all attempts at a satis- 
factory explanation of their peculiar behavior. 
They are characterized by a periodic variation of 
light of short duration. The entire cycle of change 
is usually accomplished in a few days, in some stars 
in a few hours. A very rapid rise to maximum 
brightness is followed by a prolonged drop to mini- 
mum that is sometimes interrupted by a weak at- 
tempt at an increase of brightness. This cycle of 
change is repeated continuously with clock-like pre- 
cision. 

Many explanations of the peculiar behavior of 
these stars have been suggested, though none fit all 
the requirements. According to one theory the 
peculiar light variations are due to internal oscil- 
lations of the stars resulting from collisions with 
planetary masses. 

There are also the remarkable cluster variables 
found in some of the noted globular clusters com- 
posed of thousands of stars. They resemble the 
Cepheids in the nature of their light variations, 
though the periods are extremely short. The cycle 
of change is usually accomplished in less than 
twenty-four hours. Some stars wax while others 
wane, each star keeping strictly to its own period, 
163 



SPLENDORS OF THE SKY 



entirely independent of other stars in the same 
cluster. 

This independence of each other is not so strange 
when we consider that the individual stars in the 
globular clusters are separated by distances com- 
parable to the distance that separates our solar 
system from the nearest stars and that ample room 
is furnished each star for the possession of exten- 
sive satellite families without being crowded by too 
close stellar neighbors. Why some few stars in a 
globular cluster should show this unaccountable 
periodic flickering of light while the majority shine 
with clear and steady rays is another of the unex- 
plained mysteries of this wonderful universe of 
which we form such a humble part. 



164 



CHAPTER XXI 

DRIFT OF THE STAR STREAMS 

THE sun, as is now well known, travels through 
the universe at the rate of twelve miles a 
second, or more than 1,000,000 miles a day. In a 
year it passes over four times the distance from the 
earth to the sun and after an interval of nearly 
16,000 years has journeyed the same distance 
through space that light travels in one year. 

The earth and other planets, of course, share this 
motion of their ruler, since the solar system moves 
as a unit with the relative motions and positions of 
its various members unaffected by the translation 
of the whole system through space. The revolu- 
tion of the planets around the sun, combined with 
the motion of the system as a whole, causes their 
paths through space to assume the form of cork- 
screw spirals. 

165 



SPLENDORS OF THE SKY 



In the past five thousand years practically no 
changes appreciable to the naked eye have taken 
place in the forms of the constellations or the 
brightness of the stars due to this motion of the 
sun. After an interval of one hundred thousand 
years, however, which is less than the period man 
has been known to exist upon this planet, the in- 
dividual motions of the stars combined with the 
sun's advance through the universe begins to no- 
ticeably alter the appearance of the constellations 
and the brightness of the nearer stars. 

In this time the sun travels between six and seven 
li^ht years, which is more than the distance that 
separates us from a few of the nearer stars. From 
the birth of a star to its extinction many journeys 
to and fro from one end to the other of the stellar 
system may be possible if the extent of the system 
of the stars to which we belong is limited in diam- 
eter. 

In four hundred million years, a less time than 
has elapsed since the formation of the earth's sur- 
face crust, according to some geologists, the sun 
has journeyed so far through our stellar system 
that its light will take 25,000 years to retrace the 
path. In other words the sun has travelled in this 
166 



SPLENDORS OF THE SKY 



period 25,000 light years, which is sufficient to have 
brought it from far-distant star clouds of the Milky 
Way to its present position. 

During this tremendous interval of time what 
portions of the heavens has our sun passed 
through? Has it moved in a straight line or in a 
closed orbit as do its own satellites? 

How far, moreover, has it advanced in its evolu- 
tion after pouring forth its rays of light and heat 
during this journey at a most extravagant rate 
with no sign of diminishing force? Unanswerable 
questions as yet. One fact is reasonably certain, 
however. No serious catastrophe, such as a col- 
lision with or close approach to a neighboring sun 
either dark or light, has occurred during this vast 
period. Wherever our sun has journeyed it has 
been allowed to trace its path undisturbed by out- 
side influences. 

The life process nas slowly and steadily ad- 
vanced upon the earth and possibly upon other 
planets of the solar system as well during this pe- 
riod. As far as our own planet is concerned, evi- 
dence of this undisturbed development is stored 
away in geological formations. 

Collisions or close approaches of stars are such 
167 



SPLENDORS OF THE SKY 



rare phenomena, occurring so far only in the more 
congested regions of the Milky "Way, that it is 
stated as one of the fundamental laws of the uni- 
verse that * ' the stars describe paths under the gen- 
eral attraction of the stellar system without inter- 
fering with one another. ' ' 

One of the most interesting and important prob- 
lems of modern astrophysics is to determine the 
form and extent of the system of stars to which 
we belong. A beginning at least has been made 
toward the solution of this problem. Material is 
being collected continually, day by day and year 
by year, bearing upon the number of the stars, 
their velocities both in the line of sight and across 
the line of sight, their distribution with reference 
to the plane of the Milky Way, which is recognized 
as the foundation of the system, and their physical 
characteristics as well, including relative masses, 
densities and luminosities. 

One of the most important discoveries in astro- 
physics was made through painstaking examina- 
tions of the motions of a great number of stars. 
It w r as in 1904 that the noted astrophysicist 
Kapteyn first proved in this way the existence of 
two intermingling star streams and showed that 
168 



SPLENDORS OF THE SKY 



the motions of the stars were according to law and 
order and not at random. 

More and more facts are gradually being gath- 
ered as to the nature of these two star streams. 
It has been established by this time that the great 
majority of the stars belong to one or the other 
of these two great streams. Also that the number 
of stars in the two streams are in the ratio of three 
to two and their velocities in the ratio of 1.52 to 
0.86; that is, the stars in one stream are more 
numerous and move more rapidly than the stars 
of the other stream in the above proportions. It 
has been found, moreover, that the motion of one 
stream relative to the other is parallel to the plane 
of the Milky Way, emphasizing the importance of 
this formation in the stellar system. 

It is a peculiar fact that the Orion or Helium 
stars scarcely partake of this star streaming tend- 
ency, though they show a decided inclination to 
drift in groups, all the members of a group moving 
in the same general direction and with the same 
speed. 

The Pleiades and the chief stars in the constella- 
tion Orion are notable among these moving clus- 
ters. This gregarious habit is not entirely confined 

169 



SPLENDORS OF THE SKY 



to the Helium stars, for some stars as far advanced 
as the sun in evolution show the same trait. 

The stars that most closely follow the directions 
of the two interpenetrating star streams are the 
Hydrogen stars. Their preference for these two 
streams is most marked. The older stars, espe- 
cially the red stars, show a tendency to diverge 
from the directions of the two streams. The aver- 
age rate of motion of the red stars of advanced 
age is three times as great as the extremely slug- 
gish rate of the Orion stars and their independ- 
ence of motion is much more marked, for they 
show no inclination to remain in or near the plane 
of the Milky Way, as do the earlier type stars. 

Though the two star streams to which the major- 
ity of all the stars belong represent a fundamental 
feature of the stellar system, it is believed that 
they are but a first approximation to the motions 
of the stellar system. The more recent investiga- 
tions in astrophysics, especially those connected 
with the spiral nebula? and globular star clusters 
as external systems of stars, seem to indicate the 
possibility of a spiral form for the sidereal system 
to which we belong. 

Nothing is known that contradicts this belief, 
170 



SPLENDORS OF THE SKY 



while the star streaming characteristic mentioned 
above is in line with the theory. It has been sug- 
gested by some astronomers that the dense star 
clouds of Cygnus or of Sagittarius may be the 
strongly condensed centre or nucleus of our stellar 
system and that the spiral arms lie along the plane 
of the Milky Way. Whether matter is flowing 
along the spiral arms toward the nucleus or from 
the nucleus outward along the spiral arms, streams 
of matter will flow in opposite directions where 
the arms merge into the central nucleus. 

What would be the nature of stellar movements 
in a system possessing a double armed spiral 
formation cannot be stated until the dynamics of 
motion in spirals is known. At present there is 
no clue to the law that governs such motion. 

Tf the stellar system is indeed a spiral forma- 
tion, more extended study of the relative motions 
of the stars will eventually reveal the law that 
governs their motion. It might then be possible 
to trace the path of our sun through the system of 
the stars just as it is now possible to trace the 
paths followed by his satellites within the solar 
system. 



171 



CHAPTER XXII 



THE MILKY WAY 



TO THE people of all ages and nations the Milky 
"Way or Galaxy has ever been an object of awe 
and admiration. Many beautiful though fanciful 
stories exist concerning it. It has been called both 
the Sky River and the Path of Souls. In Scandi- 
navia, where it arches magnificently through the 
zenith in winter months, it is the Winter Street, 
and another favorite name for it is Jacob's Road. 

The true immensity and grandeur of this girdle 
of the universe the human mind can hardly grasp. 
It is, as it were, the equatorial belt of the sidereal 
system and marks the outermost confines of the 
universe. The distances of the stars that belong to 
it must be measured by the thousands of light 
years. 

Suns heaped upon suns occur here in such pro- 
172 



SPLENDORS OF THE SKY 



fusion that in certain of the denser portions it is 
impossible to form any estimate of their true 
nnmber. Nebulae and star clusters as well as stars 
surrounded by nebulosity are intermingled with 
the dark lanes and stretches of inky blackness. An 
example of the latter is the Coal Sack in the South- 
ern Cross, not visible in our latitudes. These 
darker portions are as characteristic of the Milky 
Way as the bright knots and streamers of light 
so frequently met with. Many of them are truly 
rifts in the star clouds through which we see into 
space beyond, but dark nebulous matter is also 
abundant in the Galaxy, in fact nebulosity both 
light and dark is a strong characteristic of galactic 
regions. 

Here, too, tend to collect the younger members 
of the stellar system, the Wolf-Rayet or bright 
line stars, with a type of spectrum bordering upon 
that of gaseous nebulaa, and the helium stars. 
Both groups come early in stellar evolution. The 
Wolf-Rayet stars are never found anywhere except 
in the Milky Way and in the Greater and Lesser 
Magellanic Clouds, two small, somewhat circular 
regions in southern circumpolar skies very similar 
in nature to the Galaxy. The bluish-white helium 

173 



SPLENDORS OF THE SKY 



stars show a decided preference for the plane of 
the Milky Way and so also do the green or gaseous 
nebulas and the temporary stars or Novas. "With 
hardly an exception the latter have flashed out in 
the regions of the Milky Way. On the other hand, 
the white or spiral nebulas conspicuously avoid 
galactic regions and seek the neighborhood of the 
galactic poles, particularly in Virgo and Canes 
Venatici, in northern latitudes. It is believed by 
many astronomers that these spirals are not nebulae 
at all but " island universes, " as they are called, 
lying beyond our stellar universe and so distant 
that we cannot distinguish their true stellar na- 
ture. There is also the attendant theory that our 
own universe is of spiral form with its nucleus in 
some galactic region and its spiral arms in the 
plane of the Milky Way. If spiral nebulae shall 
be found on future investigation to be, in truth, 
exterior universes it will be reasonable to assume 
by analogy that our universe also has a spiral 
form. 

Counts of stars in various parts of the heavens 
have established the fact that the great majority 
of the stars in the universe crowd toward the ga- 
lactic plane, and by far the greater number of 
174 




DARK MARKINGS IN THE MILKY WAY 

(Photographed by Barnard on Mt. Wilson with the Bruce telescope) 



SPLENDORS OF THE SKY 



these are actually within the bounds of the Milky 
Way. There is a noticeable thinning out of stars 
as we approach the galactic poles and an increase 
in the number of spiral nebulae. This has led to 
the belief that the shape of our stellar universe is 
decidedly flattened in the direction of the galactic 
plane. It has been likened to a disk in shape, the 
most distant regions of the Milky Way marking 
the confines of our visible universe. It has been 
judged that our particular solar system at present 
occupies a position well within the Milky Way a 
little above the galactic plane and part way from 
its centre to its edge, far from the central aggrega- 
tions of the Galaxy. This belief is based partly 
upon the form of the Milky Way as seen from our 
viewpoint. To us it appears as a great circle en- 
compassing the heavens. 

In northern latitudes the Milky Way is never 
seen to run due north and south or east and west, 
but crosses the sky diagonally and is best seen in 
fall or late summer. In spring it lies too near 
the horizon to be well observed. From eircum- 
polar regions through Cassiopeia to Cepheus and 
into Cygnus it runs. Here it divides into two 
parallel branches for nearly one-third of its entire 

175 



SPLENDORS OF THE SKY 



length, running through Aquila, Ophmchus and 
Sagittarius to Scorpio. There the two branches 
join once more and it passes beyond our vision into 
southern skies, where it enters Centaurus and Crux, 
the Southern Cross, and traverses the magnificent 
and extensive constellation of Argo Navis, which 
contains Canopus, the second brightest star in the 
heavens. From Argo Navis it curves northward 
once more, passing close by Canis Major, which 
contains Sirius, the brightest of the stars, and 
running through Monoceros, where it is extremely 
brilliant, to Gemini and Taurus, then through 
Auriga and Perseus to circumpolar regions in the 
neighborhood of Cassiopeia once more. Through- 
out this entire course it exhibits a wonderful diver- 
sity of form and structure. We note that it in- 
cludes in its midst or passes near many of the 
brightest of the stars, while it includes an over- 
whelming majority of the fainter stars. The 
brilliancy of the Milky Way and its immediate 
neighborhood is in striking contrast to the dearth 
of stars near its poles. 

Since the stellar system is undoubtedly condensed 
toward the plane of the Milky Way and we are 
situated between the centre and the edge of this 
176 



SPLENDORS OF THE SKY 



plane, it is evident that we look through a dense 
layer or stratum of stars in the direction of the 
Milky Way. All the stars that lie in the direction 
of the Galaxy do not belong in its midst, but are at 
varying distances from us. The true aggregations 
of the Galaxy are at excessive distances and are 
for this reason extremely faint, on the average 
between the fourteenth and sixteenth magnitude, 
and probably only in a few rare cases brighter 
than the eighth magnitude. As distinct points of 
light they are beyond the reach of the unaided eye 
and give us only the impression of hazy light. 

Successful attempts have been made to portray 
various regions in the Milky Way, especially in 
Sagittarius and Cygnus, and we cannot fail to be 
impressed with the impossibility of making any 
estimate of the number of suns represented in some 
of these views. Such, moreover, is the diversity 
of form of its various parts that it has been said 
no one region can be regarded as typical of the 
entire Milky Way. The stupendous scale of this 
wonderful structure fills us with awe. Suns are 
here crowded together until they seem as countless 
as the grains of sand upon the seashore, and yet 
there is no doubt that they include among their 
177 



SPLENDORS OF THE SKY 



number some of the giants of the universe only 
dimmed to our eyes by immeasurable distances. 

We cannot fail to recognize the fact that there 
is some definite plan or purpose in this structure 
in its relation to the remaining portions of our 
universe. It is not unmeaning chaos that we look 
upon, for certain types of stars crowd toward the 
Galaxy while others avoid it, and certain physical 
characteristics are shared by all of its members. 

We can only stand awestruck before the plan 
of the universe that our minds cannot grasp or 
comprehend. 



178 



CHAPTER XXIII 

DO DARK STARS EXIST IN THE HEAVENS? 

DARK stars abound throughout the universe 
either in a solitary state or associated with 
brilliant companions. Though invisible, they have 
disclosed their presence to us in a variety of ways. 
It may never be possible to form any estimate of 
their true numbers, but we cannot doubt their 
existence. 

Many a dark or feebly luminous body of sun- 
like dimensions has been detected by the perturbed 
motion of some bright star with which it is phys- 
ically connected. Sirius and Procyon were ob- 
served to describe little ellipses under the influence 
of some unseen force long before their companions 
were discovered. The companion of Sirius, though 
not absolutely dark, is one of the most feebly lumi- 
nous bodies known. Its mass, however, is nearly 

179 



SPLENDORS OF THE SKY 



one-half that of Sirius and it has a powerful 
attractive force. 

It is now conservatively estimated that one star 
in every three is either double or multiple ; that is, 
belongs to a system of two or more stars in revo- 
lution around a common centre of gravity, and 
in numberless cases dark stars are included in 
these systems. Sometimes the components of these 
systems are so close that in the most powerful 
telescopes they appear as a single star, but their 
composite nature is revealed by the spectroscope, 
which shows a doubling or shifting of the lines 
of the spectrum. These are called spectroscopic 
binary systems. The doubling of the spectral 
lines shows a second luminous body to be present, 
but the shifting of the lines without doubling 
shows that the bright star has a companion giving 
little or no light. As the bright body recedes in 
its orbit under the sway of its dark attendant the 
lines shift toward the red end of the spectrum, 
and as it turns in its orbit so as to approach the 
earth the lines shift toward the violet end of its 
spectrum, and the amount of the shift shows the 
velocity with which it moves in its orbit. In some 
cases it is possible to determine not only the time 
180 



SPLENDORS OF THE SKY 



it takes for the star to describe its orbit and the 
velocity with which it is moving, but also the dis- 
tance between the two components in miles, their 
relative mass and brightness, and their mass and 
brightness as compared with that of our own sun. 
All this is possible, however, only in case the dis- 
tance of the system from the solar system is known. 

Stars are often variable in light due to periodical 
eclipse by dusky satellites. Such is Algol, the 
Demon Star, -Tvhose wink every three days means 
that a dark body passes before his face and shuts 
off fully five-sixths of his light. Stars that are 
regularly occulted or eclipsed by dark attendants 
form a large class of stars known as eclipsing 
variables. They furnish another proof of the ex- 
istence of dark bodies. 

It is of peculiar interest that dark stars are 
often associated with stars known to be young; 
that is, with Helium or Sirian stars. Since mem- 
bers of double star systems have presumably at 
one time formed a single mass, gradually separat- 
ing into two or more components and drawing 
further and further apart as time goes on, we 
would expect the components to show signs of 
equal age. Why should they be in so many cases 
181 



SPLENDORS OF THE SKY 



of nearly equal mass, but widely different light 
giving power? We must conclude that there are 
two classes of dark stars, those dark through old 
age coming at the end of the evolutionary stage, 
and those dark because they are imperfect ra- 
diators and have not the necessary physical prop- 
erties for keeping up long continued radiation 
without appreciable loss of light and heat. Pos- 
sibly at the time of their separation from the orig- 
inal mass there was unequal distribution of the 
materials possessing the light and heat giving prop- 
erties needed for long continued radiation. We 
can only conjecture as to the cause, but the fact 
remains that intensely brilliant stars with every 
sign of youth are physically connected with stars 
necessarily of equal age but emitting no appre- 
ciable light. Such well known bright stars as 
Sirius, Spica, Procyon and Castor are attended 
by faint or invisible companions. 

Whether there exist in space systems in which 
all the members are dark we have no means of 
knowing, but we can reasonably assume that as old 
age overtakes the brighter members of these systems 
they too will become dark. The systems of 61 
Cygni, one of our nearer neighbors, includes one 
182 



SPLENDORS OF THE SKY 



or more invisible members, and the entire system 
shows signs of great age. There seems no escape 
from the conclusion that in far distant ages the 
entire system will be devoid of light. Investiga- 
tions are also establishing the fact that the velocity 
through space of stars and star systems increases 
with age. If so, with what tremendous velocity 
extinct stars must be rushing on their mysterious 
journeys to unknown fates! 

We have been considering so far dark stars that 
are associated with bright companions. The sud- 
den blazing forth of temporary stars has led to 
the belief that dark stars occur in an isolated state 
as well. It is only when collisions between dark 
stars occur or when dark bodies pass through 
resisting nebulous matter with the attendant burst- 
ing forth of light that we can know of their exist- 
ence. 

Our own sun in his old age would be a star of 
this class. For the ruler of our solar system is 
supreme and shares his glory with no other body 
of sunlike dimensions. Our own system may be 
but one of many that have dark attendant satellites 
vastly inferior in mass to the ruling body around 
which they circulate. And when old age falls upon 
183 



SPLENDORS OF THE SKY 



the ruler of such a system and his light and heat 
have disappeared he has no choice but to join 
the host of dark stars, as cold and inert as his 
lifeless attendants that still circle ceaselessly 
around their ruler as he journeys onward to ex- 
tinction. We can only reason about the existence 
of such dark and lifeless systems through analogy. 
We see in the heavens the nebulas that give birth 
to stars. We see also young stars, and stars in 
the zenith of their splendor, such as our own sun, 
and again stars failing in light and heat with 
advancing old age; and why not cold, rayless 
stars ? 

It is known that stars exist in a non-luminous 
condition in mixed systems of light and dark stars. 
The telescope and spectroscope prove this to us. 
So it is reasonable to assume that dark bodies exist 
among the single stars. 

Dark bodies of planetary size attendant upon 
bright stars could never be detected by any means 
at our disposal, for bodies shining only by reflected 
light from a central sun and of such minute pro- 
portions compared with their luminary- would be 
hopelessly lost in his rays. It is only when a 
satellite has sunlike dimensions that it can influ- 
184 



SPLENDORS OF THE SKY 



ence the ruler of the system and reveal its pres- 
ence by the perturbations it produces. If our most 
powerful telescopes were placed at the distance of 
Alpha Centauri, the nearest star, and pointed at 
our solar system, it would never disclose the fact 
that our sun had a single attendant planet. 

It is doubtful if we can ever fulfil our very 
natural desire to know whether other stars are 
attended by worlds of planetary size. 

As regards dark suns, however, Bessel, one of 
the greatest of mathematicians, said we had reason 
to believe there may be as many dark stars as 
bright ones. 



185 



CHAPTER XXIV 

THE BRILLIANT NOVA OF 1918, NOVA AQUILiE NO. 3 

QHORTLY after the moon's shadow had swept 
^ across the United States on the 8th of June, 
1918, and while, in fact, members of many success- 
ful eclipse expeditions were busily engaged in de- 
veloping plates and packing up eclipse apparatus, 
there suddenly appeared in the heavens, in the 
constellation Aquila, the Eagle, the most brilliant 
temporary star or nova that has been seen since 
Kepler's star suddenly flashed into view in 1604, 
more than three hundred years ago. 

According to a Harvard College Observatory 
bulletin numerous telegrams were received at the 
Harvard Observatory during the night of June 8 
from all parts of the United States and Europe 
announcing the independent discovery of the nova 
by many amateur and professional astronomers. 
186 



SPLENDORS OF THE SKY 



The first person to report the discovery was Mr. 
W. H. Cudworth, who sent a telephone message 
from Norwood, Mass. Due to differences in longi- 
tude the star was probably first seen in Europe. 
Harvard observers immediately proceeded to photo- 
graph the visitor and look up its past history. 

Photographic plates dating back as far as May 
22, 1888, showed a faint star of the eleventh mag- 
nitude whose position in the heavens was identical 
with that of the nova. Several hundred plates 
were examined at the Harvard Observatory in 
order to trace the light variations of this star in 
the past thirty years. There appear to have been 
slight fluctuations in the brightness of the star 
during that period that have a range of about 
half a magnitude. 

The following facts were established from 
examination of photographs. On June 3 this 
wonderful star possessed its normal brightness for 
the past thirty years, that of a faint star of the 
eleventh magnitude. Because of clouds no plates 
were exposed on June 4, 5 and 6. On June 7 the 
star appeared as a sixth magnitude star just at the 
limit of visibility to the unaided eye. Its bright- 
ness had therefore increased one hundred fold in 

187 



SPLENDORS OF THE SKY 



less than four days. On June 8, the memorable 
day of its discovery, it had become a star of the 
0.5 magnitude and was a magnificent blue-white 
star nearly as bright as Vega, shining all the more 
resplendently since it appeared in a part of the 
heavens where few first magnitude stars appear. 

Upon June 9 Nova Aquilse No. 3, as it has been 
labelled astronomically, attained what appears now 
to have been its maximum brightness, when it 
outshone the famous Nova Persei of 1901 and prac- 
tically equalled Sirius in brilliancy. According to 
observations of Prof. E. E. Barnard, made June 9, 
its magnitude was minus 1.4, while the magnitude 
of Sirius is given as minus 1.6. 

How long it will remain visible to the naked eye 
is doubtful. Nova Persei faded from view within 
a month and was conspicuous for only a few days. 
It was unlike the present nova in being distinctly 
ruddy at maximum brightness. It is customary 
for temporary stars to fade rapidly but fitfully 
away. Kepler's star, which was nearly as bright 
as Venus at maximum brightness, was unusual 
among temporary stars in remaining visible for 
fully two years. 

The nova is situated in one of the two branches 
188 



SPLENDORS OF THE SKY 



of the Milky Way, that lie between Aquila and 
Scorpio, and it was all the more conspicuous for 
appearing in a portion of the heavens where few 
bright stars are seen. 

On June 8 the spectrum of the nova was found 
to be that of an early type star, with dark lines 
due to absorption of the light of the stellar core 
by cooler hydrogen gas surrounding the star. A 
spectrum taken at Harvard on June 9 confirmed 
the first observation and showed narrow, dark 
hydrogen lines on a nearly continuous background. 

All astronomers agree that the sudden outburst 
of novas, a rare phenomenon, is evidence of some 
sort of a celestial catastrophe, but the exact cause 
of the sudden and tremendous increase in the light 
giving powers of the star is still in doubt. The 
latest theory assumes that a dark or light star 
encounters a stream of nebulous matter, and its 
heat and light are enormously increased by the 
friction created by its passage through the nebula. 
Considerable weight is given to this theory by the 
fact that Nova Persei was observed to be sur- 
rounded by nebulous matter soon after its sudden 
appearance. Nebular conditions still exist around 
this star, which is still visible in large telescopes. 

189 



SPLENDORS OF THE SKY 



At first it was thought that matter was travelling 
outward from the star with the velocity of thou- 
sands of miles per second, but this appeared most 
unlikely, and it was finally shown that the phe- 
nomenon could be explained by assuming that the 
surrounding nebula was illuminated by the waves 
of light proceeding outward from the star. Light 
was being reflected to us from the dark nebula 
just as the planets and moon reflect the light of 
the sun. The theory of the origin of novae by 
encounters between stars and nebulous matter does 
not satisfactorily explain all that has been observed 
in connection with the appearance of these stars, 
and the origin of novae is still a subject open to 
discussion. 

The novae show no measurable parallax and 
therefore their distance is unknown, but it is as- 
sumed to be very great, certainly not less than 
300 light years, possibly in some instances, several 
thousand light years. 

The great value of preserving photographic 
records of the heavens appears in connection with 
the discovery of this star. It is possible to prove 
by reference to the photographs of this portion 
of the sky taken at the Harvard College Observa- 
190 



SPLENDORS OF THE SKY 



tory that the present nova was not a dark star 
previous to its present outburst, but a faint star 
of the eleventh magnitude, and all its past history 
for thirty years is now available. The sudden rise 
of this star to the minus one and four-tenths mag- 
nitude represents an increase in light giving power 
of about ninety thousand fold. In other words, 
when this star attained its greatest brilliancy on 
June 9 it would have taken the combined light of 
90,000 stars of its former brightness to equal it. 

Since Nova Aquilag has no measurable parallax 
it must have been before its outburst at least equal 
in brightness to our own sun. At the time of its 
outburst its light was therefore equal to the light 
of many thousand such suns as our own. It is 
possible that Nova Aquilas is situated in distant 
regions of the Milky Way where lie vast nebulous 
tracts of matter, and that even before its outburst 
it was superior to our own sun in brilliancy. 

Possibly at the time of its outburst a catastrophe 
became visible that took place several thousand 
years ago, for if the star is several thousand light 
years distant the light that now reaches us started 
on its journey many centuries ago. 

Since the date of its discovery astronomers have 
191 



SPLENDORS OF THE SKY 



obtained many spectroscopic records of the changes 
that have taken place in this brilliant nova. Fol- 
lowing the usual course of temporary stars Nova 
Aquilae No. 3 decreased fitfully but rapidly in 
brightness and in a few months became a faint 
fifth magnitude star, just perceptible to the naked 
eye. 



192 



CHAPTER XXV 

CALCIUM GAS IN THE MILKY WAY 

TW" JOVA AQUILJG No. 3, the brilliant temporary 
■*■ ^ star that suddenly burst forth June 8, 1918, 
and then rapidly decreased in brightness until it is 
now scarcely visible to the eye, has been under 
continual observation by astronomers since the date 
of its first appearance. 

A most unusual and unexpected result of the 
spectroscopic study of this star has been the de- 
tection of clouds of calcium vapor lying in the 
Milky Way between us and the new star. 

This discovery has been announced in a com- 
munication to the Observatory, a British publica- 
tion, by the prominent British astronomer Ever- 
shed, stationed at Hodaikanal, India, who reports 
the existence of fine dark lines of calcium in the 
spectrum of the nova in a normal position. Since 
193 



SPLENDORS OF THE SKY 



all the spectral lines of a nova are always greatly 
displaced and distorted, due to the abnormal con- 
ditions existing in such stars, the presence of the 
lines of any element in a normal position points 
to an origin of these lines external to the scene 
of the outburst. 

According to one of the first laws of spectrum 
analysis, upon which depends our knowledge of 
the physical condition of the stars, if light from 
a certain source, such as an incandescent solid, 
or liquid, or gas, under extremely high pressure 
(in this case the nova), passes through a cooler 
intervening gas, the latter will absorb from the 
source of light beyond the particular elements 
of which the cooler gas consists and as a result 
the spectrum of the hotter body (the nova) will 
be crossed by dark absorption lines of the cooler 
intervening gas. 

It is upon this same principle that the elements 
that enter into the composition of the cooler en- 
veloping gases of a stellar body can be determined. 
Upon the continuous band of color emanating 
from the star's interior appear the dark absorp- 
tion lines originating in the cooler atmosphere of 
the star. 

194 



SPLENDORS OF THE SKY 



Were the outer gaseous envelope of Nova 
Aquilse in a normal condition of temperature and 
pressure its absorption lines would be in their 
normal position in the spectrum, and the existence 
of these clouds of calcium vapor lying in the Milky 
Way between us and the nova would not have 
been suspected, since in that case the lines of 
calcium in the star's atmosphere and in the ex- 
terior clouds of calcium would have been coincident 
and would have been attributed entirely to a stellar 
origin. In the atmosphere of a nova, however, 
conditions are far from normal. 

A celestial catastrophe has occurred and ab^ 
normal conditions of temperature and pressure 
existing in the star's outer gaseous envelope are 
registered in the form of distorted and displaced 
lines and bands both bright and dark in the star's 
spectrum. Only the lines of calcium vapor far 
exterior to the scene of the catastrophe remain 
uninfluenced by these conditions and appear fine 
and dark with the distorted, abnormal spectrum 
of the nova for a background. Remove the nova, 
or place in its stead a normal star, and the pres- 
ence of the calcium clouds would remain unknown. 

Continuing his investigation of the calcium lines 
195 



SPLENDORS OF THE SKY 



in Nova Aquilae and looking up the records of 
past novas and a number of binary stars, which 
also show displaced lines due to the mutual revo- 
lution of the components of each system, Evershed 
made some additional discoveries of great interest. 
Observations had been recorded in the past of the 
existence of the dark absorption lines of calcium 
in the spectrum of Nova Persei, which appeared 
in 1901 and closely rivalled Nova Aquilae in 
splendor. 

The lines of calcium also appeared in their nor- 
mal position in this nova, though all the other 
lines of its spectrum were displaced. A few binary 
stars also showed the calcium lines in a normal 
position, though all lines originating in the atmos- 
phere of these stars were displaced owing to 
mutual revolution of the components of these star 
systems which produces periodic displacements of 
all their spectral lines. Evershed concluded as a 
result of his observations of all these stars, ten 
or twelve in number scattered over widely sepa- 
rated regions, that there exists in the Milky Way 
vast clouds of calcium vapor through which the 
light of these stars passes before it reaches our 
eyes, and he also concluded as a result of further 
196 



SPLENDORS OF THE SKY 



investigations that these clouds lie virtually sta- 
tionary in space. So immovable do they appear 
that he considers they would furnish a valuable 
method for a new determination of the motion of 
our own sun through space. 

It has long been known that vast clouds of 
nebulous matter exist in the Milky Way, but this 
is the first time that the presence of a gaseous 
tract of matter has been detected by absorption 
lines produced in the spectrum of a star far 
exterior. It is a most unique and unusual dis- 
covery, and shows what valuable and unexpected 
results may be obtained from spectroscopic observa- 
tions of the stars. Under ordinary circumstances, 
the existence of these vast clouds of calcium vapor 
would be unknown and unsuspected. 

A normal stellar spectrum would not reveal 
their presence. Yet the rays of light from Nova 
Auuilae and Nova Persei, as well as certain binary 
star systems, have not only told the secret of the 
physical condition of these stars but have also 
brought us the proof of encounters with interven- 
ing gases on their long journey through space to 
the solar system and our own planet. 

An interesting and valuable field for future 
197 



SPLENDORS OF THE SKY 



study has thus been indicated. Observations of 
other stars with displaced spectral lines may 
enable astronomers to detect the presence of clouds 
of gas lying between us and such stars and to 
determine in addition whether these clouds of 
vapor are at rest or drifting through space. 

Why calcium vapor should exist in such pro- 
fusion in space is a mystery. As is well known to 
astronomers, there is a certain type of stars known 
as calcium stars, whose spectra are characterized 
by the presence of strong absorption lines of cal- 
cium, indicating that calcium vapor occurs in great 
abundance in the atmosphere of such stars. To 
this class of stars belongs Canopus, one of the 
greatest suns of the universe, and Procyon, a near 
neighbor of the solar system, which is a"bout ten 
times more luminous than the sun. 

In addition to dominating the spectra of stars 
of this class calcium is found in great quantities 
in the solar type stars, to which our own sun be- 
longs, and less conspicuously in later type stars. 
It is only in the helium and hydrogen stars that 
this element appears to be absent. The distribu- 
tion of this element in the atmosphere of the sun 
can be studied by means of the spectro-heliograph, 
198 



SPLENDORS OF THE SKY 



which makes it possible to photograph the sun in 
the light of a single spectral line. 

The circulation of calcium vapor in the sun's 
atmosphere has been extensively studied by this 
method, and it has been noted as a singular and 
puzzling fact by astronomers interested in solar 
research that the vapors of this comparatively 
heavy element are frequently found at very high 
levels in the sun's atmosphere. 

It is, moreover, a noteworthy fact that this ele- 
ment, which apparently occurs in the greatest 
abundance in stars of many types, and, as is now 
known, exists in different portions of the universe 
in the form of vast clouds, is also of the greatest 
importance upon our own planet, earth. 

It is this element that enters into the structure 
of the bones and is so essential to virtually all 
forms of animal life. Though its particular impor- 
tance in the fashioning of the stars and in the 
universe as a whole is unknown, it is certain that 
without it animal life as it now exists on our 
planet would be impossible. 



199 



CHAPTER XXVI 

THE SPIRAL NEBULA AND THE GREAT NEBULA IN 
ANDROMEDA 

^F^HE discovery in recent years of a number of 
•*■ novae, or temporary stars, in spiral nebulae is 
regarded by astronomers as a matter of unusual 
importance since it may have a direct bearing 
upon the baffling problem of the nature, size and 
distance of these peculiar spiral formations now 
known to exist in the heavens in numbers running 
into the hundreds of thousands, if not millions. 

It would in no wise lessen our interest in the 
most famous of all spirals, the Great Andromeda 
Nebula, to discover that it is an " island universe' ' 
consisting of millions of suns as well as vast nebu- 
lous formations and star clusters similar to those 
found in the Milky Way of our own system. 

According to astronomers who have made a spe- 
200 



SPLENDORS OF THE SKY 



cial study of these spiral formations, dimensions 
and distances of a higher order than that of the 
stars are to be expected for the spiral nebulae if 
they are remote universes 

The marked distribution of all stars, star clus- 
ters and gaseous nebulae within our own universe 
with reference to the Milky "Way, or Galaxy, has 
long been known. In or near this plane are to be 
found the majority of all stars, bright as well as 
faint — though the condensation is more marked 
for faint stars — showing that our system is de- 
cidedly flattened toward the plane of the Galaxy. 
The tendency of the gaseous nebulae and the plan- 
etary nebulae, as well as the vast star clouds and 
tracts of irregular nebulous formations, dark as 
well as light, to adhere closely to the neighbor- 
hood of the Galaxy is well known. 

In marked contrast to this we find that the spiral 
nebulae actually avoid the regions of the Milky 
Way and are found in greatest abundance in parts 
of the heavens farthest removed from galactic re- 
gions; and, what is of special interest in this con- 
nection, all temporary stars discovered up to the 
present time, about thirty in number, have been 
closely confined to the Milky Way, with but three 
201 



SPLENDORS OF THE SKY 



exceptions. One of these, T Coronae, was not a 
typical nova. The other two were found in spiral 
nebulae and were the only temporary stars known 
to exist in spirals until quite recently, when Prof. 
Kitchey at Mount Wilson discovered a nova in the 
spiral nebula N. G. C. 6946. 

The discovery of this nova, the third to be 
found in a spiral, caused a suspicion that there 
might be an actual physical connection between 
the spiral formation and the star. The probability 
that three temporary stars should chance to be in 
line with spiral nebulae was very small. The dis- 
covery of this nova led to a reexamination of 
former photographs of spiral nebulae with the 
result that eleven temporary stars were found 
in spiral nebulse as against twenty-six previ- 
ously found in the Milky Way. Throughout the 
remainder of the heavens temporary stars are non- 
existent. 

Another extremely important point brought out 
by astronomers in connection with the discovery 
of these temporary stars in spirals is the great 
difference in the brightness of the novae in spirals 
and the novae in the Milky Way. Temporary stars 
that have appeared in the Milky Way have usually 
202 




THE GREAT SPIRAL NEBULA IN ANDROMEDA 

(Photographed by Ritchey with the 2-ft. reflector of the Yerkes Observatory) 



SPLENDORS OF THE SKY 



been somewhat sensational objects, in some cases 
appearing at their maximum fully as brilliant as 
the brightest of the stars or even the planets 
Jupiter or Venus. The novae in spiral nebulae, on 
the contrary, are excessively faint objects, averag- 
ing about the fifteenth magnitude, entirely invisible 
at their maximum brightness except in the most 
powerful telescopes. 

Between the average brightness of the temporary 
stars appearing in the Milky "Way and those de- 
tected in spirals there is a difference of fully ten 
magnitudes. If we assume that the two classes of 
novae are about the same in actual luminosity this 
great difference in apparent brightness is due to 
differences in distance. A difference of ten mag- 
nitudes in apparent brightness of two stars that 
are in reality of equal light giving power means 
that the fainter star is one hundred times more 
distant than the brighter. We have no knowledge 
of the actual distance from us of the temporary 
stars situated in or near the Milky Way, but it is 
believed to be very great, probably in many cases 
as high as several thousand light years. This 
would place the spirals at distances to be measured 
by hundreds of thousands of light years and give 
203 



SPLENDORS OF THE SKY 

support to the theory that they are " island uni- 
verses" of millions of suns. 

Even with the sixty-inch reflector of the Mount 
"Wilson Observatory no star in the heavens fainter 
than the twentieth magnitude can be detected. 
Photographs of spirals taken with this instrument 
show no individual stars, but nebulous, starlike 
condensations analogous probably to the nebulous 
star clouds of our own Galaxy, its star clusters 
and its nebulous formations. The appearance of 
a temporary star of the fifteenth magnitude in a 
spiral nebula would therefore mean the appear- 
ance of a star that is at least several hundred 
times brighter than the brightest individual star 
in the nebula, while the nova of 1885 in the Great 
Andromeda Nebula, which was of the seventh mag- 
nitude at maximum and therefore almost visible 
to the naked eye, must have attained an actual 
luminosity hardly to be equaled by the combined 
light of a million of the brightest stars in the 
heavens. 

Dr. Shapley has pointed out that this unusual 

case would have a parallel in our own Galaxy, 

however, if we make the assumption that Nova 

Persei, the famous temporary star of 1901, is situ- 

204 



SPLENDORS OF THE SKY 



ated in some one of our most distant galactic clouds. 
The noted temporary stars of Hipparchus and 
Tycho Brahe may have originated in far distant 
galactic regions for all we know to the contrary. 
If so they burst forth with a temporary splendor 
equal to several million such suns as our own. 

Though the question of the true nature of spiral 
nebulae is still an open one, the appearance of 
extremely faint novas in their midst must be con- 
ceded to be a strong argument in favor of the view 
that they are far distant external universes of the 
order of magnitude of our own stellar system and 
of the attendant theory that our own universe, 
composed of some hundreds of millions of stars 
and nebulous formations, luminous as well as non- 
luminous, has a spiral formation with the double 
branching spiral arms to be traced among the 
star clouds of the Galaxy. Upon the assumption 
that the spirals are far distant universes, the fact 
that they so conspicuously avoid galactic regions in 
strong contradistinction to nearly all other classes 
of objects in the heavens is explainable. If they 
are situated at distances more remote than other 
celestial objects the vast tracts of nebulous matter, 
dark and light, in galactic regions and the dense 
205 



SPLENDORS OF THE SKY 



star clouds that abound in this plane would hide 
from view spirals lying near the Milky Way. 

Were our own system of stars as far away as 
the Great Nebula in Andromeda it would appear 
very much as the Great Nebula in Andromeda 
does to us. Without telescopic aid it would be 
seen as a faint patch of light about the size of the 
full moon. When viewed with the most powerful 
telescopes its most brilliant individual stars would 
still remain hopelessly invisible, but various nebu- 
lous condensations of light would appear, suggest- 
ing conglomerations of many stars and nebulae. 
Our own little sun at this distance would be 
beyond the range of all telescopes. There would 
be little reason to suspect we were viewing a uni- 
verse of hundreds of millions of suns or that all 
these suns were in unceasing motion in obedience 
to the mysterious laws governing their formation 
and that of the universe to which they belong. 

Since the Andromeda Nebula is exceptionally 
large, it is either comparatively near or an unusu- 
ally large formation. Many of the spiral nebulae 
are extremely faint. They appear in the greatest 
abundance in the heavens. Of the fainter nebulas 
virtually nothing is known. The thought that these 
206 



SPLENDORS OF THE SKY 



faint spirals may be aggregations of suns at dis- 
tances to be measured by hundreds of thousands 
of light years is staggering to the imagination of 
man. 



207 



CHAPTER XXVII 

GASEOUS NEBULA AND THE ORIGIN OP THE STARS 

*T*HE gaseous or green nebulae, so named from 
-■■ the greenish tinge imparted to them by the 
presence of the unknown gas nebulium, present 
problems to the astronomer as interesting and im- 
portant as those connected with the noted spiral 
nebulae. These two types of nebulae are radically 
different in their composition and in their distri- 
bution in the heavens. 

Gaseous nebulae are beyond a doubt members of 
our own system of stars. They crowd densely 
toward the Milky Way, the groundwork of our 
universe. The spirals as conspicuously avoid it. 
The latter, it is suspected, may be systems of 
stars independent of and external to our own. 
The gaseous nebulae we think of as the material 
from which the stars are fashioned. 
208 



SPLENDORS OF THE SKY 



Their extent is enormous. We have as yet no 
definite idea of their distance, but it must be as 
great as that of the nearer stars. Most probably 
they occur in greatest profusion among the more 
dense star clouds of the Milky Way at distances 
to be measured by thousands of light years. In 
many cases they must occupy an interval of space 
so great that light would require many years to 
cross it. 

Vast gaseous nebulae enwrap, in some instances, 
moving clusters composed of many stars such as 
the Pleiades and the stars of Orion. The Great 
Orion nebula is the finest of all the gaseous nebula?. 
Double, triple and multiple stars are enmeshed in 
its extensive folds. 

The extreme tenuity of the gaseous nebulas is 
as astonishing as their vast extent. One ten thou- 
sand millionth of the density of our own atmos- 
phere at standard pressure is one of the estimates 
of the density of the denser portions of the Great 
Nebula in Orion. 

It is difficult to imagine the condition of matter 

in such an extreme state of rarefaction. Yet these 

nebula? assume an infinite variety of form and 

structure. In addition to the vast nebula? of 

209 



SPLENDORS OF THE SKY 



irregular form there are the ring or annular nebulae, 
peculiar formations probably spheroidal in form, 
with a star of variable luster often shining with- 
in the ring. There are the Saturn nebula, 
the Owl, Crab, Dumb-bell, North America and 
many other odd shaped gaseous nebulae frequently 
named from their fancied resemblance to objects 
familiar to terrestrial inhabitants. 

There are also the planetary nebulae, a species 
of gaseous nebulae named from their resemblance 
to faint planetary disks, that are receiving consid- 
erable attention at the present time. Astronomers 
find their extremely high velocities of motion in 
the line of sight which average twenty-four miles 
a second surprising and extremely puzzling. 

In the scheme of stellar evolution the first type 
stars, on the border between nebulous and stellar 
conditions, are supposed to follow the planetary 
nebulae in order of development, but the very high 
velocity of the planetary nebulae would hardly 
connect them with the slowly moving new stars. 
It has been found that the stars move more rapidly 
with increasing age and we should therefore have 
to place the planetary nebulae at the end of the 
evolutionary chain instead of the beginning, if we 
210. 



SPLENDORS OF THE SKY 



consider simply the very high speed with which 
they are moving through space. 

Some recent investigations of these same planet- 
ary nebulae show that they are rotating as well and 
that in two special cases the periods of rotation 
lie between 600 and 14,000 years and the masses 
of the rotating nebulas between three and 100 times 
that of the sun. 

The planetary nebulas are usually strongly con- 
densed toward their centres. Here are found the 
denser helium and nebulium gases, while hydro- 
gen occurs chiefly near the outlying portions. 

These three gases, hydrogen, helium and nebu- 
lium, are the elements always to be found in the 
gaseous nebulas, whether irregular or planetary. 
They enter into the composition of all nebulas ex- 
cept the spirals, which shine on the other hand 
with "white" light and give the continuous spec- 
trum of incandescent solids or liquids or gases 
under high pressure. They are for this reason 
often referred to as the white nebulae, as opposed 
to the green or gaseous nebulae. The latter show 
the typical nebular spectrum consisting of bright 
lines of the three gases mentioned. 

A bright line spectrum indicates that the source 
211 



SPLENDORS OF THE SKY 

of the illumination is gaseous matter at low pres- 
sure. The green nebulae are very feebly luminous 
and the nature of their luminosity is one of their 
most puzzling features. According to a recent 
theory the mysterious element nebulium is some 
familiar element electrically excited. Some 
astronomers believe that the luminosity of the 
gaseous nebulae is chiefly due to electrical excite- 
ment of certain portions. In all these nebulae 
occur dark portions as well as light. The illumi- 
nation is locally condensed and certain portions 
seem for some inexplicable reason to have lost their 
illuminative power. This would hardly be ex- 
pected if the luminosity of the gaseous nebulae 
were due to light of incandescence alone. A more 
uniform distribution of light would be expected. 
It is generally believed that the temperature of 
the gaseous nebulae is extremely low and if due 
to electrical discharges their average temperature 
might approximate to absolute zero. 

Tremendous extent, extremely low density and 
marked feebleness of light are the three peculiar 
characteristics of the gaseous nebulae. 

Evidently plan and purpose control the nebulae 
as well as the stars. They do not represent mean- 
212 



SPLENDORS OF THE SKY 



ingless chaos, but form one of the links in the chain 
of evolution. 

It is not by chance that stars, both single and 
multiple, are found in the midst of the vast irreg- 
ular nebulae, while even the small planetary 
nebulae, the annular nebulae and the nondescript 
nebulae have in nearly all instances stars closely 
associated with them. 

It has been pointed out by some astronomers 
who are inclined to question the transformation 
from nebulae to stars that the nebulosity connected 
with these stars may rather result from gradual 
change of stars into nebulae, and that the nebu- 
losity surrounding the Pleiades and the stars of 
Orion are rather emanations of gaseous matter 
from these stars and that eventually they will all 
be dissipated into nebular form. It has been 
pointed out also in this connection that flames of 
hydrogen and helium often burst forth from the 
solar surface at the rate of 200 miles per second 
even under present conditions, while a velocity of 
ejection of 380 miles per second would permit 
them to leave the surface of the sun never to 
return. 

The nebulous matter now to be found surround- 
213 



SPLENDORS OF THE SKY 



ing the famous temporary star, Nova Persei, is 
instanced in support of the view that stars may be 
dissipated gradually or suddenly into a nebulous 
state. 

Although the existence of dark nebulae closely 
resembling the luminous variety in form seems to 
show that some nebulae at least may become extinct 
without passing through the usually accepted or- 
der of evolution from nebulae to star, the theory 
that gaseous nebulae do not condense into stars 
would leave the question of the origin of stars en- 
tirely unsettled. That there is a continual cycle 
of change from nebulae to star and possibly also 
from star back to nebulae by chance encounter of 
one star with another or close approach of two 
stars seems more in accord with observed condi- 
tions. The passage of a star through a stream of 
dark nebulous matter would doubtless result in 
such nebular conditions as are observed in the case 
of the temporary stars, Nova Persei, Nova Aquilae 
and others. 

Man is handicapped in his observations of the 

nebulae by the fact that changes in the form and 

structure of these objects are so extremely slow. 

A hundred or a thousand years is but a moment in 

214 



SPLENDORS OF THE SKY 



the life of a nebula. It is, therefore, next to im- 
possible to detect a progressive change in any one 
nebula that would show whether condensation or 
expansion is taking place. 

The spectroscope has furnished much valuable 
information concerning the gaseous nebulas. In 
fact, practically all we know about these objects 
has been obtained with the aid of the spectroscope. 
We trust also that it will eventually solve the mys- 
tery of the strange gas nebulium that is the most 
characteristic element of the gaseous nebulas. The 
fact that it is unknown elsewhere but adds to the 
mystery. The condensation of the gaseous nebulas 
into stars and the final transformation of stars 
back to nebulas through chance encounters and col- 
lisions pictures a state of universal and continual 
change, a universe without beginning or end, and 
in absence of proof to the contrary this is generally 
believed to be the true cycle of change that is tak- 
ing place among the stars. 



215 



CHAPTER XXVIII 

THE GREAT STAR CLUSTER IN HERCULES 

\ N extensive study of the great star cluster in 
•*■ *■ Hercules, in connection with other globular 
star clusters, has been made at the Mount Wilson 
observatory and results seem to indicate that the 
parallax of this noted cluster is less thain one-ten- 
thousandth of a second of arc, and that it is at a 
distance of 37,000 light years, with a diameter of 
several hundred light years. 

This faint wisp of light, barely visible to the un- 
aided eye on clear, dark, summer nights, thus takes 
on the dimensions of a sidereal universe sepa- 
rated from us by immensities of space so vast that 
our minds utterly fail to grasp them. Thirty- 
seven thousand years ago then, if the above esti- 
mates are correct, the light that now comes to us 
from this gorgeous assemblage of suns started forth 
216 



SPLENDORS OF THE SKY 



on its journey at the rate of 186,000 miles a sec- 
ond, and if the cluster were suddenly blotted out 
of existence another 37,000 years would elapse 
before our solar system would fail to receive its 
light. 

Only the rnosv powerful telescopes are capable 
of completely resolving the Hercules cluster into 
its stellar components. Of more than 5,000 stars 
counted upon one photograph fully 4,000 were 
fainter than the thirteen and one-half magnitude 
and, therefore, invisible as separate stars in small 
telescopes. Long photographic exposures made 
with the largest reflecting telescopes bring out 
great numbers of extremely faint stars in this clus- 
ter lying near the limit of visibility of these great 
instruments. 

When we consider that the entire space covered 
by the Hercules cluster is only about one-sixteenth 
of the area of the full moon, it seems almost in- 
conceivable that this insignificant little patch of 
light represents a mighty assemblage of suns. 

A peculiar distribution of stars has been noted 
in the Hercules cluster. The brighter stars extend 
outward from the centre in curved lines, while the 
extremely faint stars show a uniformly globular 

217 



SPLENDORS OF THE SKY 



distribution. Three dark lanes making an equian- 
gular juncture near the centre of the cluster were 
detected many years ago and later photographs 
show a similar formation repeated at other points, 
which implies the existence of some definite law of 
formation. 

The Hercules cluster is considered the finest 
globular cluster in the northern heavens, though it 
is surpassed in splendor by two clusters in the 
southern hemisphere in the constellations Centau- 
rus and Tucana. Over 6,000 stars have been 
counted in the Centaurus cluster within a space 
about as large as that filled by the full moon, and 
they average about twelve and one-half magnitude, 
a magnitude brighter than those in the Hercules 
cluster. In this cluster, also, many extremely faint 
stars are present. The globular cluster in Tucana 
is somewhat smaller than the Centaurus cluster and 
contains about 2,000 bright members that are, how- 
ever, more closely crowded together than are the 
members of the cluster in Centaurus. The globu- 
lar cluster in Tucana, which is a constellation near 
the South Pole, is regarded by some as the finest 
object in the heavens. The dark lanes noticeable 
in the Hercules cluster are entirely absent in the 
218 



SPLENDORS OF THE SKY 



two southern clusters, which show a decided cen- 
tral crowding of the brighter stars as well as of 
the extremely faint members. 

The distance of the Lesser Magellanic Cloud, 
which appears very much like a star cloud de- 
tached from the Milky Way, but which lies too far 
from the plane of the galaxy to be considered a 
portion of this girdle of the heavens, has been es- 
timated at 30,000 light years. The Milky Way, 
which defines the outer limits of our own sidereal 
system, is generally believed to consist of several 
branches lying one beyond the other. The nearer 
portions, it is estimated, lie somewhere between 
3,000 and 15,000 light years distant. Estimates 
of the distance vary, according to whether or not 
we include stars as bright as the sixth magnitude 
among the hosts of stars that crowd these regions. 
The vast majority of stars that form the star dust 
of the galaxy range from the fourteenth to the six- 
teenth magnitude. It is interesting to consider in 
this connection that a star 10,000 times as luminous 
as the sun would appear as a ninth magnitude 
star at a distance of 20,000 light years. If we ad- 
mit the presence of stars brighter than the ninth 
magnitude in the nearer portions of the Milky 
219 



SPLENDORS OF THE SKY 



Way we must either admit the presence of veri- 
table giants in our sidereal system, stars that are 
even more than 10,000 times as great as our own 
sun in brilliancy, or we must limit the extent of 
our stellar system and assume that the nearer star 
clouds in the galaxy are but 2,000 or 3,000 light 
years distant. 

A class of objects far more numerous than the 
globular star clusters that lie at immeasurable dis- 
tances are the spiral nebulae, often spoken of as 
the white nebulas, to distinguish them from the 
green or gaseous nebulae. The idea that these are 
external sidereal systems or "island universes' ' has 
recently been revived. Many years ago, before 
the day of large telescopes and of the spectroscope, 
it was believed that all nebulae were star clusters 
that could be resolved into separate stars by tele- 
scopes of sufficient power, but when the larger tele- 
scopes were obtained it was found that they could 
not resolve some of the nebulae into star clusters, 
and finally along came the spectroscope to prove 
the truly gaseous nature of the green nebulae. As 
to the nature of the spiral nebulae, however, we are 
still in doubt. The spectroscope simply tells us 
that they have a type of spectrum known as "con- 
220 



SPLENDORS OF THE SKY 



tinuous," which may belong to a solid or 
liquid substance at high temperature or to an in- 
candescent gas under high pressure. In this case 
the spectroscope refuses to give us any informa- 
tion. 

We are familiar with the idea that our solar 
system is evolved from a nebula, but the spiral 
nebulas to which we refer are far too vast to give 
birth to anything as simple as a single sun and its 
satellites or even to arise, on the other hand, from 
the close approach of two stars. Nothing less than 
clusters of suns could be evolved from nebula? as 
extensive as these. The evolution of groups of 
stars from irregular gaseous nebula?, such as the 
Orion nebula and the nebula surrounding the 
Pleiades, is a process now going on before our 
eyes. There are also moving clusters of stars, such 
as the Taurus cluster, which is known to include 
thirty-nine stars far exceeding our own sun in size 
and splendor, that may have evolved from one 
nebula. The latter star cluster has been very ex- 
tensively studied and it has been estimated that in 
something like 65,000,000 years it will appear as an 
ordinary globular star cluster about twenty min- 
utes in diameter, or two-thirds the diameter of the 
221 



SPLENDORS OF THE SKY 



full moon, if it keeps up its present rate and di- 
rection of motion. 

If future investigations of spiral nebulas shall 
disclose the fact that these formations that occur 
in such great numbers are indeed far beyond the 
limits of our own universe and form isolated stellar 
systems, as now appears to be the case with the 
Hercules star cluster, light may be thrown upon 
some perplexing questions that arise concerning the 
form and extent of our own sidereal system. Ac- 
cording to some astronomers a spiral form for our 
own stellar system fits in better than any other 
with all the known facts concerning it. 



222 



CHAPTER XXIX 

WONDERS OF THE GLOBULAR STAR CLUSTERS 

INVESTIGATIONS made in the past few years 
by Dr. Harlow Shapley at the Mount Wilson 
Solar Observatory in regard to the distances and 
distribution of about seventy globular star clusters 
have brought results amazing even to the astrono- 
mers themselves, accustomed though they are to 
dealing with inconceivably great intervals of space 
and time, and have greatly broadened our ideas of 
the form and extent of the visible universe. 

The following facts respecting these wonderful 
star systems have been gleaned from several ex- 
tremely interesting articles by Dr. Shapley, ap- 
pearing in recent publications of the Astronomical 
Society of the Pacific, which are preliminary to 
complete discussions of the observations and re- 
sults now in process of publication. 
223 



SPLENDORS OF THE SKY 



Globular star clusters are, as the name implies, 
symmetrically shaped, globular, in some cases ellip- 
soidal, systems composed of thousands, possibly 
hundreds of thousands, of individual stars strongly 
condensed toward the centre. A few of these clus- 
ters are visible to the naked eye as faint patches of 
light, and the largest of them appear to fill a space 
in the heavens less than that occupied by the full 
moon. 

The most noted of these are the great cluster in 
Hercules in the Northern Hemisphere and Omega 
Centauri and 47 Tucanae in the Southern Hemi- 
sphere. The last named cluster is, in fact, 
considered by some to be the finest telescopic object 
in the heavens. 

Indeed, the telescope makes a most striking 
transformation in the appearance of these hazy 
patches that we strain our eyes to see on a clear 
night. A most brilliant assemblage of thousands 
of suns, some deep red, others blue-white, gleam 
and flicker, some with steady intensity, others with 
the periodic pulsation of light that is characteristic 
of the cluster variables. 

It is the periodic waxing and waning of the light 
of the cluster variables that has furnished the clue 
224 



SPLENDORS OF THE SKY 



to the distances of the globular star clusters, though 
the results have been checked by comparing the 
apparent luminosities of other stars in the clusters 
of the type of the red giant stars, such as Antares 
and Betelgeux, and of the blue-white type of Vega 
and Rigel with the known luminosity of these stars 
at a standard distance from the sun. 

The brightest stars in the globular clusters have 
been found to have a surface temperature two or 
three thousand degrees less than that of our sun, 
and to be much redder in color. Emitting as much 
light as they do, their volume must be very great. 
They correspond to the red giants of the Galaxy. 

The blue-white stars of the clusters are two or 
three magnitudes fainter than the brightest red 
stars, and among the bluer of these stars are found 
the cluster variables which are similar in their 
light variations to the noted Cepheid variables of 
the Galactic system. Their light, color, spectrum 
and velocity in the line of sight all pass through 
a marked periodic variation in less than a day. 

The maximum brightness is more than twice the 

minimum, but the average brightness for a star of 

this short period type has been found to be almost 

exactly one hundred times the luminosity of our 

225 



SPLENDORS OF THE SKY 

own sun. Between two and three hundred typical 
variables whose periods range from a few hours to 
one hundred days have been chosen from five glob- 
ular clusters, the small Magellanic cloud, and the 
Galaxy to form a curve which shows that the lum- 
inosity of a variable star of this class bears a simple 
relation to the period of its variation of light. 

It has been found that the variables with periods 
less than one day average one hundred times the 
brightness of the sun, while those with the longest 
periods average nearly ten thousand times the lum- 
inosity of the sun and are rarely surpassed in 
brightness by other stars. 

The important result of this relationship is that 
it gives immediately the distance of stars of this 
type as soon as their apparent brightness and the 
period of their fluctuations of brightness are known 
and if the variables are located in globular clusters 
it gives the distances of the clusters. 

Investigations of the light variations of the Ce- 
pheid variables in the small Magellanic cloud a 
few years ago gave a distance of about 33,000 light 
years for this object, which was about the greatest 
distance the mind of man was asked to grasp until 
the measurement of the distances of the globular 
226 



SPLENDORS OF THE SKY 



clusters was undertaken by the same methods. 

An apparently hopeless task has at last been ac- 
complished and within the short period of two 
years the distances of sixty-nine globular star clus- 
ters have been measured with a probable error not 
exceeding twenty per cent, of the values given, 
which compares favorably with the degree of ac- 
curacy obtainable in measuring by direct methods 
the parallax of our nearer stellar neighbors within 
a distance of one or two hundred light years. 

One-fourth of the globular star clusters meas- 
ured are more distant than one hundred thousand 
light years. The two nearest, Omega Centauri and 
47 TucanaB, are a little less than 23,000 light years 
away. 

The most distant so far known has a parallax 
found by one method to be .000015 seconds, and 
by another method .000014 seconds. Either value 
would place it at a distance from us of considerably 
more than 200,000 light years. 

Possibly before the human race appeared upon 
this planet the light that now reaches our eyes from 
the most distant globular clusters had started on 
its journey. 

The individual stars visible in the globular clus- 
227 



SPLENDORS OF THE SKY 



ters, though actually from 100 to 10,000 times more 
brilliant than our sun, appear extremely faint be- 
cause of their great distance. Their apparent mag- 
nitudes usually average from the twelfth to the 
seventeenth, while the twenty-first is the limit of 
visibility of the greatest telescope. Were our sun 
in the nearest of the globular clusters it would be 
too faint to be visible. The stars that gleam faintly 
in these clusters are the giant suns of their sys- 
tems. 

How many more there are too faint to be seen 
is unknown. The diameters of the globular clus- 
ters average several hundred light years. There is 
nothing in the neighborhood of our sun to compare 
with this dense crowding of huge suns into a com- 
paratively small space. Within a distance of 
thirty-three light years of the centre of one typical 
globular cluster there are to be found 15,000 stars 
one hundred or more times brighter than our own 
sun. 

Within the same distance of the solar system 
there are known to be but four or five such stars. 
Yet these individual stars in clusters are sepa- 
rated by distances comparable to the distance that 
separates our own sun from Alpha Centauri, more 
228 



SPLENDORS OF THE SKY 



than four light years away, and no collisions be- 
tween stars in globular clusters have yet been re- 
corded, though, of course, all individual members 
of the system are in motion. 

The distribution of the globular clusters with 
reference to the plane of the Galaxy or Milky Way 
is most striking. Of the sixty-nine clusters exam- 
ined (and the survey is considered complete within 
one hundred thousand light years of the sun), 
thirty-two are north of this plane and thirty-seven 
south of it, and the average distance of the clusters 
from the plane is about twenty-two thousand light 
years. The centre of the system of clusters lies in 
the Galaxy in the region of the dense star clouds 
of Sagittarius and the diameter of the system is 
at least three hundred and twenty-five thousand 
light years, since two known clusters are separated 
by this distance. The distance of our local group 
of stars from the centre of this enormous system is 
about sixty-five thousand light years. 

A significant characteristic of the system of 
globular clusters, Dr. Shapley points out, is the 
equatorial belt between 10,000 and 12,000 light 
years wide within which no globular clusters are 
to be found. Within this belt are nearly all the 
229 



SPLENDORS OF THE SKY 



stars listed in our catalogues, including the stars 
visible to the naked eye as well as the gaseous nebu- 
las, diffuse nebulosities and open star clusters. 
Outside the belt are the globular star clusters, the 
Magellanic clouds, a few isolated stars and prob- 
ably the spiral nebulae. 

The explanation offered for the avoidance of the 
equatorial belt by the globular clusters is their in- 
ability to form and exist as compact organizations 
in such an intense gravitational field. 

The conclusions drawn from the facts so far dis- 
covered are that all known objects in the heavens 
belong to one enormous unit. The globular clus- 
ters, Magellanic clouds and probably spiral nebu- 
lae as well, though vast systems composed of thou- 
sands, possibly hundred of thousands, of stars, 
and moving through space with velocities of a 
higher order than the average stellar velocity, are, 
nevertheless, subordinate members of an organized 
system whose form and extent the globular clusters 
roughly outline. 

The volume of this vast organized system is more 
than 100,000 times that formerly assigned to the 
stellar system. 

The present location of our solar system in the 
230 



SPLENDORS OF THE SKY 



universe is about three hundred light years from 
the centre of a loosely formed moving star cluster 
which lies just north of the plane of the Milky 
Way and about half way from its centre to its 
edge. 

Man no longer places himself at the centre of the 
universe, but finds it 65,000 light years away. 



231 



CHAPTER XXX 



THE LIFE OF A STAR 



^T^HE discovery of radioactive substances has 
-*• radically affected many astronomical theories 
bearing not only upon the age of the sun and its 
planet family, but also upon the evolution of the 
stars in general and the periods of time required 
for the various stages of their development. 

It is believed, moreover, that there are certain 
properties of matter, as yet unknown as the revo- 
lutionizing properties of radium were unknown 
until the end of the nineteenth century, that will 
solve the great problem of the source of the radiant 
energy of the stars and explain why these bodies 
pour forth into space light and heat and life-giving 
energy at a lavish rate that has shown no signs of 
abatement during hundreds of millions of years. 

It is now known, thanks to the irrefutable evi- 
232 



SPLENDORS OF THE SKY 



dence furnished by radio-active substances, that 
certain rocks containing uranium and the products 
of its disintegration, helium and lead, have been 
in existence for at least 1,500,000,000 years. How 
long prior to this date our planet earth possessed 
a surface crust is not known. 

According to the testimony of geologists based 
upon examination of the oldest fossil-bearing rocks, 
well differentiated forms of life were in existence 
on our planet a billion years ago. 

During this inconceivably long interval of time, 
according to astronomers, our sun must have main- 
tained its energy of radiation virtually constant 
though possibly varying cyclically within narrow 
limits, for any marked increase or decrease in the 
radiant energy of the sun would have made impos- 
sible the continuous development of the various 
forms of life that we know has taken place during 
this period. 

This fact has a direct bearing on the evolution 
of the stars or their transition from one type to the 
next. It is generally assumed that the helium or 
bluish-white stars are the youngest and that they 
change gradually to the next type, the hydrogen 
or white stars, then to the yellow or solar type and 
233 



SPLENDORS OF THE SKY 



finally to the orange and red stars that are ap- 
proaching extinction. 

The transition from one type to the next in 
order is supposed to be attended by a decided 
though gradual decrease in the light and heat-giv- 
ing power of the star that amounts to several 
hundred per cent, and would be fatal to life upon 
any possible planet system of the star. 

Astronomers have found from a consideration of 
all known sources of energy, including radio-activ- 
ity, that twenty-five million years is all that can 
be allowed for the evolution of our sun from a 
nebular state through the various spectral types to 
its present condition, that of a star in the zenith 
of its development. 

This conclusion is, of course, not at all in accord 
with any of the observed facts either of astronomy 
or geology and simply shows that the true source 
of the energy of the stars has not yet been dis- 
covered. 

Whatever the source of the solar energy may 
prove to be, it has been sufficient to keep the spec- 
tral type of our sun and its light and heat unvary- 
ing, except within comparatively narrow limits, 
for at least one billion years. 
234 



SPLENDORS OF THE SKY 



For this reason astronomers are inclined to be- 
lieve that the gradual transition from one star type 
to another, granted such a transition does take 
place, is a matter of hundreds of millions rather 
than millions of years. 

Since primitive forms of life first appeared upon 
earth, our sun and its satellites have travelled more 
than 100,000 light years, that is, as far as light 
would travel in 100,000 years with its unimag- 
inable velocity of 186,000 miles in a second, and 
has experienced no catastrophe, though it has 
doubtless journeyed far and wide through the star 
streams of the Milky Way and seen the apparently 
immovable constellations fade away in the distance 
and new groupings take their place. 

Though our own particular sun has so far es- 
caped catastrophe the sudden appearance of Novae 
is proof that all stars do not pursue the normal 
course of evolution. As measured by man's stand- 
ards of time temporary stars or Novse appear in- 
frequently. 

Novae of startling splendor such as Nova Aquilae 
of the year 1918 are to be looked for only at inter- 
vals of many years, running at times into centuries, 
but less conspicuous temporary stars appear on 
235 



SPLENDORS OF THE SKY 



an average of one in every three or four years. 

Many of these do not even attain visibility to the 
unaided eye at their best, but this is probably due 
rather to their comparatively great distance than 
to marked deficiency in actual luminosity at the 
time of their outburst. 

Since a year is but a moment in the life of a uni- 
verse, Novae are by no means rare phenomena aside 
from man's point of view. Since the time when 
life on our planet was in its early infancy, possibly 
1,500,000,000 years ago, 400,000,000 temporary 
stars have burst forth, if the present rate of their 
appearance was maintained in the past. 

Four hundred million celestial catastrophes have 
been enacted during this period. Nova Aquilae No. 
3, the famous temporary star of 1918, has under- 
gone in a few short months rapid and irregular 
transitions of type such as normally would require 
hundreds of millions of years if we judge by the 
apparent permanency of type of our own sun dur- 
ing the past 1,500,000,000 years. 

At first appearance a brilliant blue-white star of 

helium type, Nova Aquilse later appeared as yellow 

as Capella and at another time more reddish than 

Aldebaran, a late type star, though no regular pro- 

236 



SPLENDORS OF THE SKY 



gression of type occurred, the changes being fitful 
and irregular. Little is known yet concerning the 
origin of Novae. 

According to a suggestion of Prof. William H. 
Pickering, Novaa may arise from the impact of a 
body of planetoidal dimensions with a star, assum- 
ing that groups of such bodies are possibly drift- 
ing through space in great profusion and the va- 
rious members are separated by many millions of 
miles. In the regions of the Milky Way, where the 
star material occurs in greatest profusion, encoun- 
ters would be most apt to occur. 

There is the possibility, according to certain as- 
tronomers, that our sun may have acquired part 
of his planet family by capture. Our planet must 
have possessed a surface crust for nearly two bil- 
lion years at least. It has been proven that its in- 
terior is not viscous, but as rigid. as steel, and is 
probably composed of material very closely resemb- 
ling meteorites in composition. 

The discovery of radio-active substances has ex- 
ploded the idea that the only source of the inherent 
heat of the earth is its originally high temperature 
and that it is simply cooling off from a molten be- 
ginning. 

237 



SPLENDORS OF THE SKY 



The earth's temperature increases about one de- 
gree in temperature for every 100 feet in depth. 
This was formerly believed to indicate that the 
earth was cooling off gradually. It is now 
known that this heat arises from the disinte- 
gration of radio-active substances in the earth's 
crust, which sets free an enormous quantity of 
heat. 

It has been estimated also from the amount of 
heat generated by these radio-active minerals at 
the surface that the radio-active layer of rocks 
probably extends only to a depth of thirty miles. 
Beneath this crust, it is believed, there lies to a 
depth of several hundred miles material similar to 
the stony meteorites in composition, while the 
earth's central core is of metallic composition, re- 
sembling that of iron meteorites and is entirely free 
from radium. 

There is apparently nothing either in the pres- 
ent composition of the earth or in its past condi- 
tion throughout a period of over a billion and a 
half years to particularly favor the idea that it 
once formed part of a primitive solar nebula. 
Neither is there reason to believe that the sun itself 
was appreciably nearer to a nebular condition a 
238 



SPLENDORS OF THE SKY 



billion and a half years ago than it is in the pres- 
ent age. 

There is a possibility that the fate of a Nova 
may await our own sun. Its journeys through the 
universe may at some future time carry it through 
the more densely crowded portions of the Milky 
Way, where some dusky mass may chance across 
its path and suddenly terminate in a flaring out- 
burst of light and heat the long career of the beau- 
tiful yellow star that has so long supplied its planet 
family with life-giving energy. 

Under such circumstances all forms of life on its 
satellites would be extinguished in the twinkling 
of an eye. Barring this celestial catastrophe, all 
present indications point to a future existence for 
our little planet for many hundreds of millions of 
years under the genial rays of a constant sun. 



339 



CHAPTER XXXI 

STELLAR EVOLUTION AND THE " MISSING LINK" STAR 

T% J" ANY light years distant from the earth, in 
*" the vicinity of the Milky Way, is to be found 
a class of stars remarkable for their deep red color. 
If Sirius and Vega are the diamonds among the 
celestial jewels, then these unusual stars are the 
garnets and the rubies. 

For many years these carbon stars or Type N 
stars, as they are technically called, appeared to 
have no place in the evolutionary system of the 
stars. A sequence in the development of all other 
classes of stars had been well established, which we 
will briefly outline in order to show the relation- 
ship of the carbon stars to stars of other types. 

Beginning with the gaseous nebulae, the accepted 
order of stellar evolution is from nebulae to extinct 
stars through a continuous series of changes, the 
240 



SPLENDORS OF THE SKY 



first change being made from nebulae to bright line 
stars, whose type of spectrum consists chiefly of 
bright bands of unknown origin and a few bright 
lines of hydrogen upon a faint, continuous back- 
ground of rainbow color. 

These stars are spoken of as the Type O stars or 
the Wolf-Rayet stars, and they occur almost ex- 
clusively in the Milky Way. The faint, continuous 
background implies the presence of gases under 
high pressure, which form the growing nucleus of 
the star, while the bright lines and bands emanate 
from incandescent gases under low pressure sur- 
rounding the stellar core or possibly gases under 
strong electrical excitement. 

Gradually this type merges into the Orion, or 
Type B, stars, in whose spectra the bright bands 
have disappeared. The bright hydrogen lines be- 
gin to diminish in intensity and gradually fade 
away and the dark lines of helium and hydrogen 
appear. This type is often called the helium type, 
because of the prominence of the lines belonging 
to this element. The continuous background is 
particularly rich in blue and violet light, which 
gives the stars of this class their beautiful blue- 
white color. 

241 



SPLENDORS OF THE SKY 



Rigel is a magnificent star of the Helium or 
Orion type. The increase in the number of dark 
lines in the stellar spectra from this point on im- 
plies that the gases in the stars' atmospheres are 
now absorbing more and more from the source of 
light beneath the rays of the elements of which 
they themselves consist, according to one of the first 
laws of spectrum analysis. 

The dark lines are for this reason often spoken 
of as absorption lines, and they appear dark only 
by contrast with the brilliant background of con- 
tinuous light upon which they are projected. As 
the composition of the stellar atmosphere changes 
with the advance in evolution, absorption lines and 
bands and flutings of various different elements 
appear, but to a given element always belongs the 
same set of lines and its own position in the spec- 
trum. 

As the Orion, or Type B star, gradually changes 
to the Sirian or Hydrogen type, the lines of helium 
diminish in intensity, while the hydrogen lines in- 
crease and finally become the most conspicuous 
feature of the type. Technically this group is re- 
ferred to as the Type A stars. The name Sirian is 
given to it also from the fact that the most bril- 
242 



SPLENDORS OF THE SKY 



liant of all stars, Sirius, is an illustrious member. 

These stars are noted for the intense whiteness 
of their light and their high temperatures, as well 
as the low density of their atmospheres. In this 
class the metallic lines of the solar spectrum also 
begin to appear faintly, and in the succeeding type 
known as the Calcium, or F type, they show more 
strength, though they still remain inferior to the 
hydrogen lines. The calcium lines have become 
conspicuous and characterize the type. 

Canopus is a most noted member of this group. 
The color of the stars from this point on is tinged 
more and more with yellow. The next step in stel- 
lar evolution is that occupied by our own sun. 
Stars of this class, are called Type G stars. In 
these the hydrogen lines are still very con- 
spicuous, but equalled in intensity by many of 
the metallic lines, which now appear in great 
numbers. 

Capella is also a prominent member of this class. 
This stage probably represents the zenith of stellar 
development, the middle-aged period of star life. 
From this point the stellar spectrum becomes more 
and more reddish as the rays of shorter wave length 
become absorbed more and more in the gases of the 
243 



SPLENDORS OF THE SKY 

star 's atmosphere, which is gradually increasing in 
density. 

Type K, that immediately follows the solar type, 
is characterized by spectra in which the hydrogen 
lines are now becoming fainter than some of the 
metallic lines. These stars are orange in color. 
An illustrious star of this type is Arcturus. Even 
before this stage there is manifest a marked ten- 
dency of the stars to divide into giants and dwarfs, 
which becomes still more pronounced in the fol- 
lowing class of red stars of Type M, which comes 
at the end of the process of evolution. 

The dwarfs of this class are so feebly luminous 
that they seem to mark the last stage before ex- 
tinction and the advent of dark stars. 

A decided decrease in the star's temperature is 
evidenced by the appearance of flutings and bands 
in the spectrum, due to metallic compounds, chiefly 
of titanium oxide. Though it is generally considered 
that the dwarf red stars of this class are nearing 
extinction, many believe that the giants of Type M, 
of which Antares and Betelgeux are well known 
examples, are stars of low density that are grad- 
ually increasing in temperature and passing 
through the evolutionary process in reverse order. 
244 



SPLENDORS OF THE SKY 



After reaching the white-hot hydrogen or helium 
stage it is held that they will pass once more 
through the solar stage to the type of dwarf red 
stars. 

Though the direction of progression through the 
various types is a matter of some uncertainty for 
certain stars, the fact that there is a gradual change 
in the life history of the average star as outlined 
above appears to be beyond question. Type merges 
into type through gradations so slight that it is 
difficult to say where one type ends and the next 
begins. 

Until recently stars of the carbon type appar- 
ently had no place in this scheme of evolution. A 
gap seemed to separate them from stars of other 
types. Though presenting some points of resemb- 
lance to the red stars of Class M, they presented 
as many points of difference. Both in general dis- 
tribution in the heavens and in type of spectra they 
refused to be classified with the M stars. 

The carbon stars are all extremely faint stars, 
due to their tremendous distance from us, even the 
brightest of the class being barely visible to the 
naked eye. They show a most marked preference 
for the plane of the Milky Way, never being found 
245 



SPLENDORS OF THE SKY 



at any great distance from it, while the red stars 
of Type M are noted for their nearly uniform dis- 
tribution in space, being found as often near the 
poles of the Milky Way as in its plane. 

Some of the M stars are our close neighbors, 
while the brightest of the carbon stars show no 
parallax or motion across the line of sight. Their 
spectra are characterized by the presence of dark 
bands due to carbon compounds, which fade away 
toward the blue end of the spectrum, while the 
spectra of the M stars have bands of titanium oxide 
sharply denned on the violet side and fading to- 
ward the red. 

In recent years the carbon stars have been care- 
fully studied, and it now appears to be well estab- 
lished that they can be traced back in evolution to 
stars of the same type as the sun along an inde- 
pendent branch. 

The discovery of a new type of star, called Type 
R, that appears to come intermediate in develop- 
ment between the solar and carbon stars, possess- 
ing some of the characteristics of each, has led to 
this conclusion. 

Stars of this new type supply the miss- 
ing link necessary to trace the development 
246 



SPLENDORS OF THE SKY 



of a solar star into a carbon star, or possibly the 
reverse. 

Spectra of more than sixty stars belonging to 
this intermediate class have been investigated. 
Many of them were formerly classified as carbon 
stars, though some have a decidedly yellowish tinge 
and partake strongly of the features of the solar 
stars. 

There are then two paths that a star may follow 
after it has reached the point in its development 
known as the solar stage. Differences in the rela- 
tive amounts of certain elements in the atmosphere 
of stars may determine which path shall be fol- 
lowed after this point, whether a star shall pass 
through Type K to a red star of Type M, whose 
spectrum is dominated by compounds of titanium 
oxide, or through the new Type R stars to red 
carbon stars, whose spectra show the distinctive 
bands of carbon compounds. 

That the carbon stars can be linked to the evolu- 
tionary chain of stellar development is particularly 
satisfying to the astronomer, for it shows that all 
stars can be included in one great system of evolu- 
tion and pass from one type to the next gradually 
as they increase in age and development. 
247 



CHAPTER XXXII 

DWARF STAR HOTTER THAN THE SUN 

*T* HE existence of a tiny body two or three hun- 
-"- dred per cent, hotter than the sun, yet with 
a diameter only one-hundredth as great, situated 
only thirteen light years distant from the earth, 
and, therefore, one of our nearest stellar neigh- 
bors, is a most interesting recent discovery of 
astronomy. 

Yan Maanen, of the Mount Wilson Solar Ob- 
servatory, noted the extremely high proper motion, 
or motion across the line of sight, of this star, and 
concluding, therefore, that it was most probably 
comparatively near to our solar system, made a 
determination of its parallax from a series of six- 
teen photographic plates. 

The value found, two hundred and forty-four 
248 



SPLENDORS OF THE SKY 



thousandths of a second of arc, is very large, the 
greatest parallax known, that of Alpha Centanri, 
the nearest star, being only seventy-six hundredths 
of a second. There are in all hardly a score of 
stars that have larger parallaxes than this small 
body and are, therefore, nearer to us. 

The motion of this star across the heavens is also 
exceptionally great, amounting to slightly over 
three seconds of arc a year. It is, therefore, the 
most rapidly moving star discovered since Bar- 
nard's Runaway Star of 1916, which is also a very 
near neighbor of ours, six light years distant and 
a very faint body as well, possessing only five ten- 
thousandths of our own sun's brightness. 

It is, however, a whole stellar magnitude, or two 
and a half times brighter than the newly discovered 
sun, which has, accordingly, only one five-thou- 
sandth part of the luminosity of our own sun and 
is one of the faintest stellar bodies known. 

The most surprising fact discovered about this 
diminutive sun is that its faintness is due to its ex- 
tremely small size and not to failing light. This is 
known from the fact that its type of spectrum is 
the Calcium or F type, which belongs to bodies at 
least two or three times hotter per unit area than 
249 



SPLENDORS OF THE SKY 



our own sun. The color of this small sun has also 
been determined and is white, indicating a high 
surface temperature. 

Since the light-giving power of this star relative 
to the sun is known, and since it radiates two or 
three times more brilliantly per unit area, it is 
possible to determine the actual size of its radiat- 
ing surface and therefrom its diameter relative to 
the sun's diameter. 

This diameter is found to be approximately one- 
ninetieth of the sun's diameter, or nine thousand 
five hundred miles. As far as size goes, it might, 
therefore, take its place among the smaller satel- 
lites of our sun, the terrestrial planets Earth and 
Venus being scarcely inferior to it in size. Yet 
this dwarf sun rushing through space is intrinsic- 
ally a far hotter body than our own sun, judging 
from its type of spectrum. 

Strange to say, the mighty Canopus, estimated 
to be at least ten thousand times more brilliant 
than the sun, has identically the same type of spec- 
trum. 

Since the dwarf sun recently discovered has 
only one five-thousandth part of the light-giving 
power of the sun, we have here two stars of iden- 
250 



SPLENDORS OF THE SKY 



tically the same temperature per unit of surface 
area, differing at least fifty million times in lu- 
minosity. Such is the disparity existing in the 
actual sizes of the suns of the universe ! 

The only escape from the above conclusions 
would lie in considering that stars with identically 
the same type of spectrum do not radiate with equal 
intensity. It is assumed to be one of the funda- 
mental laws of spectrum analysis, however, that two 
bodies with identical types of spectra radiate with 
equal intensity per unit of surface area. 

How such a tiny sun could continue to radiate 
light and heat at the lavish rate indicated by its 
type of spectrum for any great interval of time is 
a problem. Most faint stellar bodies so far discov- 
ered in the vicinity of the sun belong to the group 
of nearly extinct dwarf stars low in surface tem- 
perature and decidedly reddish in hue. This bril- 
liant little sun of calcium type, whiter and hotter 
than our own sun, is a marked exception. 

It is by far the smallest body of its type so far 
discovered. In absolute magnitude it is exceeded 
by all known stars with the exception of a faint 
companion star of Alpha Centauri. It is possible 
that this tiny sun may possess still more diminutive 
251 



SPLENDORS OF THE SKY 



satellites of its own and dispense its light and heat- 
giving rays to these smaller bodies. 

Within our own solar system, at least, it is the 
exception rather than the rule for bodies to be un- 
attended by satellites. "Were this small sun at- 
tended by any body at all comparable to it in size, 
however, its presence could be detected by its dis- 
turbance of the bright body. 

How many of these suns of planetary size exist 
in the universe it is impossible to estimate. It is 
only the very nearest of such stars that can pos- 
sibly be detected. At a distance of only thirteen 
light years the star discovered is invisible in small 
telescopes. Were it much further removed, it 
would be invisible even in large telescopes. Mil- 
lions of these diminutive suns may exist in far dis- 
tant parts of the universe, hopelessly beyond our 
reach. It is only the light of exceptionally large 
suns that reaches our eyes from far distant realms. 

Since the number of stars of the thirteenth ap- 
parent magnitude to which this sun belongs is 
estimated at something like two million, it can be 
judged that only through some marked peculiarity 
would such a star be singled out for observation. 

In general the faintness of a star is assumed to 
252 



SPLENDORS OF THE SKY 



be an indication of great distance. Very distant, 
faint stars appear immovable in the heavens, 
though they may be in reality in rapid motion 
through space. It is, therefore, convenient in many 
kinds of astronomical work to determine the posi- 
tion of some object under observation relative to 
one of these fixed " landmarks ' ' of the sky. 

It is only occasionally, as in the present instance, 
that one of these points of reference shows any 
individual motion and thereby calls attention to its 
unusual nearness. In observing the stars the as- 
tronomers have given their attention first to the 
more brilliant and conspicuous stars. The fainter 
and less noticeable stars have received less atten- 
tion and have largely escaped detailed investiga- 
tion because they are far more numerous than the 
brighter stars and to examine them with anywhere 
near the same degree of thoroughness is a manifest 
impossibility. 

The brighter a star the more likely it is to be 
classified and studied. It is only in recent years 
with the advent of powerful telescopes and photo- 
graphic methods of observations that the careful 
study of the fainter stars has been undertaken at 
all exhaustively. Interesting and important facts 
253 



SPLENDORS OF THE SKY 



regarding the fainter stars are now being slowly 
accumulated in spite of the fact that their numbers 
run into the millions and they are observable only 
with the larger instruments. 

The importance of the discovery of all facts 
possible concerning the smaller as well as the 
larger suns of the universe is very great, since by 
this means light is thrown upon many puzzling 
problems associated with the origin and evolution 
of the stars, the source of their energy and their 
varied physical characteristics as well as their num- 
bers and distribution through space. 

It is a decided addition to astronomical knowl- 
edge to know that it is possible for a body no 
larger than our own planet Earth to maintain a 
surface temperature far hotter than the sun, 
though how this tiny sun keeps up its tremendously 
high temperature is inconceivable unless there is 
assumed to be some unknown source of the radiant 
energy of the stars. 



254 



CHAPTER XXXIII 

PHOTOGRAPHY OF THE HEAVENS 

THE photography of the heavens has become of 
such importance in all branches of astronomy 
that there is hardly an observatory to-day that is 
not provided with facilities for carrying on this 
valuable work. 

Every year hundreds of photographic plates are 
exposed in the study of celestial objects, and prob- 
ably not a day passes that the sun is not photo- 
graphic plate is particularly sensitive to the violet 
over the world. The discoveries already made by 
photography have more than repaid the efforts that 
have been made to bring celestial photography to 
the highest degree of efficiency. Since the photo- 
graphic rays are particularly sensitive to the violet 
end of the spectrum, every advantage has been 
taken of this fact, and by means of specially dyed 
255 



SPLENDORS OF THE SKY 



plates it has also been possible to photograph be- 
yond the visual limit, even in the red end of the 
spectrum. 

In astronomical photography the telescope takes 
the place of the camera and the photographic plate 
takes the place of the observer at the eye end of 
the telescope. 

It is of the greatest importance in such photo- 
graphic work to accurately compensate for the 
effect of the earth's rotation on its axis, and this is 
done by means of the clockwork that is connected 
with all large telescopes, so that the axis of the 
telescope may be given a motion opposite to the 
direction of the earth's rotation. In this way all 
objects in the field of view are kept immovable with 
respect to the eye or photographic plate, and the 
telescope "follows" the object in its apparent west- 
ward motion. Anyone who has looked through a 
telescope when the clockwork is not running knows 
how rapidly an object will drift out of the field on 
account of the earth's rotation. It is customary 
when photographs of the heavens are taken to fol- 
low the object with the eye as well, by means of a 
visual telescope attached to the photographic tele- 
scope. By this means any slight irregularity of 
256 



SPLENDORS OF THE SKY 



motion can be at once detected and corrected for 
during the time of exposure. In exposures of sev- 
eral hours' duration the rate of the clock might 
affect the motion of the telescope sufficiently to 
render the photograph worthless. Exposures of 
four or five hours are frequent, and in the photo- 
graphy of a magnificent spiral nebula in Canes 
Venatici, made at the Mount Wilson Observatory, 
an exposure of more than ten hours was given. 

In photographing comets which have a percep- 
tible motion of their own during the time of ex- 
posure the telescope is made to "follow" the comet, 
that is the comet is held immovable in the field of 
view of the telescope, and star images in the field 
then appear as short trails of light instead of the 
sharply defined round dots they would other- 
wise be. 

Excellent comet photographs have been taken 
since photography of the heavens has become gen- 
eral and research work into the nature of comets is 
done now almost entirely by means of photography. 
A large number of plates are examined and com- 
pared and the entire history of a comet can be 
studied in this way from the time when it appears 
as a faint nebulous object, through the interesting 
257 



SPLENDORS OF THE SKY 



phase when it is approaching or receding from 
the sun and developing an extensive tail, until it 
again departs into the depths of space. It can be 
detected on the photographic plates long after it 
is beyond the reach of the most powerful tele- 
scopes visually. 

Many comets as well as asteroids and faint satel- 
lites are now discovered by photography. Plates 
are exposed to various parts of the heavens where 
the existence of such objects is suspected and the 
earth's motion is exactly balanced by means of the 
siderial clock so that when the plates are devel- 
oped each star registers its position by a clear, 
sharp dot proportional to its brightness. If any 
moving object is within the field it will appear on 
the plate as a short trail of light proportional in 
length to its motion during the time of exposure. 
In this way it is easily distinguished by its appear- 
ance. A host of asteroids have been discovered by 
this method and the some comets are found in 
the same way. Halley's comet at its return in 
1910 was first detected upon the photographic 
plates. Objects too faint to be seen in the largest 
telescope will cast enough light upon a photo- 
graphic plate in several hours' exposure to reveal 
258 



SPLENDORS OF THE SKY 



their presence in the heavens. Several satellites dis- 
covered photographically have never been seen ex- 
cept on photographic plates. 

These are too faint to be visible to the human 
eye aided by the most powerful telescope, and we 
owe to photography alone our knowledge of their 
existence. The eye surpasses the camera, however, 
in observation of the finest details of planetary 
and lunar phenomena, and it has been said that 
photographs taken with powerful telescopes do not 
show the detail observable visually. 

The study of all solar phenomena has been con- 
sidered of such importance that there now exist 
observatories that make this their chief work. A 
noted observatory of this class is the Mount "Wilson 
Observatory at Pasadena, Cal. Wonderful progress 
has been made here photographically. The spectro- 
heliograph was invented here by Dr. Hale and is a 
device for photographing the sun by the light of a 
single wave length such as a calcium or hydrogen 
ray. The spectro-heliograph acts as a screen to cut 
off all light except that of a certain line in the 
spectrum, and extremely valuable and interesting 
photographs of the sun have been obtained by this 
method. 

259 



SPLENDORS OF THE SKY 



On total solar eclipse expeditions the photo- 
graphic outfit is of prime importance. At this 
time only is it possible to obtain photographs of 
the mysterious corona that is only one-tenth as 
bright as full sunlight and therefore masked at all 
other times by the glare of the sun. 

A striking instance of the value of photography 
to astronomy is the discovery made by Prof. 
Barnard through the examination of photographic 
plates of a star of the eleventh magnitude in the 
constellation Ophiuchus that has the enormous 
motion through space of at least ten seconds of arc 
a year. This puts it first in the class of ' ' runaway 
stars," which, according to the late Prof. New- 
comb, have a motion that not all the matter in the 
universe could control. The greatest known annual 
proper motion, as it is called, has been 8.7 seconds 
until the discovery of this star, but very few stars 
are known that have a proper motion greater than 
one second, and the average is far below one sec- 
ond. This discovery was confirmed by the study 
of photographic plates at Lick and Harvard dating 
back as far as 1888. We have here a specific case 
of the value of photographic records. 

The astronomers of to-day are storing away 
260 




o 2 

< a 
§ 

O 
u 

w 
« 



SPLENDORS OF THE SKY 



upon photographic plates material that will lead 
to the discoveries of the future. If such valuable 
records could have been left to us by our ancestors 
the knowledge of the wonders of the heavens would 
be advancing to-day by leaps and bounds. In all 
research work into the nature and structure of the 
universe photographic records are invaluable. By 
comparison of plates taken many years apart 
changes become evident. It is believed that nebulas 
may possibly change greatly in form in the course 
of a few hundred years and that the brightness 
of many stars, aside from the class of variables, 
may have changed appreciably in this time. 
Photography is by far the best means of solving 
such questions as well as many others of a similar 
nature. Four-fifths of all spectroscopic work, it is 
estimated, is now done photographically and done 
far better than it would be possible to do it visu- 
ally, owing to the light gathering power of the 
sensitive plate. Spectra of stars that would never 
be seen otherwise can be detected by this means. 

Last but not least is the fact that the wonders 
of the telescope, the nebula?, star clusters, planetary 
markings, corona and numerous other equally inter- 
esting phenomena would never be seen except by 
261 



SPLENDORS OF THE SKY 



a few if it were not for photography. At the 
different observatories in this country, Lick, Har- 
vard, Yerkes, Mount Wilson and many others, not 
to mention those abroad, magnificent photographs 
have been taken which are at the disposal of all 
of us through our schools and libraries. To be 
sure the result may be that many of us are only 
the more desirous to see for ourselves the beauties 
of the heavens and to explore the depths of space, 
and it is to be hoped that the day may come when 
each city will have an observatory at the disposal 
of all who may care to use it. It is surprising 
what even a six-inch telescope will reveal and we 
do not need a 40-inch Yerkes telescope to enjoy 
the wonders and beauties of the universe. 



262 



CHAPTER XXXIV 

THE PHOTOGRAPHIC PLATE- 

*T*HE astronomer of to-day spends very little 
■*• time gazing at the stars through the telescope. 
His place at the eyepiece has been taken by that 
silent sentinel of the sky, the photographic plate, 
which is on duty in some instances for hours at a 
time gathering precious rays of light from star 
or nebula that the human eye would search for in 
vain. We find the modern astronomer oftener in 
the dark room, the physical research laboratory, 
the instrument shop or the computing room than 
at the telescope. His discoveries are now rarely 
made by direct observation of the heavens. They 
result chiefly from careful examination and meas- 
urement of photographs. 

Photographs taken on June 7, 1918, at the Har- 
vard College Observatory, where the photography 

263 



SPLENDORS OF THE SKY 



of the heavens is carried on regularly and systemat- 
ically every clear night, show that the initial stages 
in the rapid increase in brightness of the magnificent 
new star of 1918, Nova Aquilse No. 3, were recorded 
by this means even before the star became visible 
to the naked eye. When the brilliancy of the nova 
on the night of June 8 amazed all observers the 
astronomer's first thought was to obtain photo- 
graphs as quickly as possible of both the star and 
its spectrum and then examine its past history. 
This, it was found, had been recorded for fully 
thirty years on photographic plates stored away at 
the Harvard Observatory, where many a valuable 
astronomical discovery has been made by means of 
photography. 

A never failing eye is kept on the heavens in 
the form of the photographic plate, and changes 
that take place there hour by hour, day by day 
or year by year may be recorded for future refer- 
ence. Photographs taken in our day may be of 
priceless value to future generations of astrono- 
mers, for by comparison of photographs taken at 
intervals of ten, fifty or one hundred years impor- 
tant discoveries may be made concerning the mo- 
tions of the stars through space, changes in the 
264 



SPLENDORS OF THE SKY 



structure of the nebulae, the appearance and dis- 
appearance of temporary stars, and all the varied 
and wonderful phenomena of a universe of count- 
less suns at all stages of development. 

Celestial photography is beset with many diffi- 
culties and presents many problems, some depend- 
ent upon the nature of the plate and its develop- 
ment, others upon the instrument. 

Photographic plates are subject to many imper- 
fections. False stars frequently appear after ex- 
posure of the plate. It is not known whether these 
appear in the process of development or are due to, 
defects in the plate itself. They are usually easily 
distinguished from true stars, however. In a few 
rare instances defects in the plate have been taken 
for asteroids or comets, which usually appear aa 
short trails. 

The photographic discovery of an asteroid with 
a satellite by Prof. Wolf of Heidelberg, announced 
in the spring of 1918, caused considerable interest 
at the time, as it was most unusual and unexpected. 
Diligent search by other astronomers and the ex- 
amination of additional plates taken of the same 
region failed to confirm the discovery, and it was 
finally decided that the "satellite" was possibly 
265 



SPLENDORS OF THE SKY 



an imperfection of the photographic plate, thougri 
the discovery of the asteroid was confirmed. 

The photographic images of the stars are not of 
uniform shape and density all over the plate. They 
are usually perfectly round and of even density in 
the centre of the plate, lut near the edges they are 
elliptical or elongated and irregular in density, a 
fact that makes their accurate measurement very 
difficult. Star images are, in fact, affected by 
many different factors, depending upon the kind 
of plate used, length of exposure, temperature and 
developer, as well as the telescope itself, whether 
reflector or refractor, of short or long focal lengths. 

It is a well known fact, however, that the sizes 
of the star images on the same plate vary with the 
brightness of the stars photographed. The brighter 
the star the greater the diameter of its image on 
the plate. This affords a method of determining 
the relative brightness of the stars photograph- 
ically that is more accurate than the visual method. 
The human eye is more liable to error than the 
photographic plate, since the individual peculiari- 
ties of the eye are many and subject to great 
uncertainty. Another advantage of the photo- 
graphic method for finding the relative brightness 
266 



SPLENDORS OF THE SKY 



of the stars lies in the fact that stars too faint 
to be seen appear on the photographic plate even 
with an exposure of short duration, while a longer 
exposure brings out additional stars. 

The photographic plate, as is well known, is 
particularly sensitive to rays of short wave length, 
the blue and violet rays, while the eye is, on the 
contrary, susceptible to the rays of long wave 
length, the red, orange and yellow rays. A very 
important application of this principle is made in 
determining the color of stars so excessively faint 
that they cannot be studied with the spectroscope. 
The physical condition and stage of development 
of a star are closely associated with its color and 
therefore any knowledge that may be gained in 
regard to the color of faint stars will add mate- 
rially to our knowledge of them. 

If an excessively faint star appears much 
brighter photographically than it does visually 
it is evident that it is particularly strong in blue 
or violet light ; that is, it is an early type or young 
star. On the other hand, if the star is fainter 
photographically than it is visually it is strong 
in red or orange light, to which the eye is par- 
ticularly sensitive. Such a star is a red or late 
267 



SPLENDORS OF THE SKY 



type star. This difference between the visual and 
photographic brightness of a star is called its color 
index, and it is of great value in classifying faint 
stars, the only clue in fact that the astronomer 
possesses to their age and physical condition. It 
indicates the relative proportions of light of dif- 
ferent wave lengths emitted by the star and the 
nature of its atmosphere. 

By the use of specially dyed plates or color 
screens it has become possible to shut off the 
rays of violet or blue light from the photographic 
plate and make it sensitive to the same rays that 
affect the eye. In this way the photographic plate 
becomes the equivalent of the human eye with the 
added advantage of being free of the individual 
peculiarities of vision that make visual estimates 
of the relative brightness of the stars so uncertain. 
The stellar magnitudes determined with these spe- 
cially prepared plates are spoken of as photo-visual 
magnitudes. 

The relative magnitudes of the stars are thus 
expressed in three different scales, the visual, the 
photo-visual and the photographic. The first two 
should be approximately equal. The photography 
of the heavens with the photo-visual rays opens a 
268 



SPLENDORS OF THE SKY 



comparatively new field of investigation and ex- 
periments with various methods of dyeing plates 
or screening off certain rays may yield some valu- 
able results in the future. 



269 



CHAPTER XXXV 

THE STORY OF A RUNAWAY STAR 

^"T"*HE recent discovery of a rapidly moving star 
■*- in the constellation Ophiuchus aroused con- 
siderable interest in the astronomical world. The 
unusual motion of this star was detected by 
Prof. Barnard at the Yerkes Observatory in 1916 
from a comparison of a series of photographs taken 
at Yerkes and reaching back as far as 1894. It 
was confirmed by numerous plates taken at Har- 
vard Observatory, the earliest of which dates back 
to 1888. 

In one year this star moves about twice as far 
as the average star does in a century. It has the 
enormous proper motion, that is, motion perpen- 
dicular to the line of sight or across the sky, of 
10.3 seconds a year. If a star moves two-tenths of 
270 



SPLENDORS OF THE SKY 



a second a year it is considered to have a large 
proper motion. 

So slight is the change in the relative positions 
of the vast majority of stars from year to year 
that after the lapse of a thousand years the skies 
are practically the same in their general appear- 
ance. 

The smallest displacement that a keen eye can 
detect in the position of a star when unaided by a 
telescope is three minutes of arc, and the average 
cross motion of a star in a thousand years does 
not exceed one minute. 

The extremely few stars that form notable ex- 
ceptions are generally spoken of as "runaway 
stars. ' ' The faint star in the southern hemisphere 
known only by its catalogue name of Cordoba Zone 
5th No. 243 formerly headed the list of runaway 
stars with a proper motion of 8.70 seconds, and 
next in order is the famous runaway star Groom- 
bridge, 1830, with a cross motion of 7.07 seconds. 

So rapid is the motion of Barnard's star that it 
will cover an arc of fully three degrees, just the 
length of the belt of Orion, in a thousand years. 
If the majority of stars had a motion at all com- 
parable to this the appearance of the constella- 
271 



SPLENDORS OF THE SKY 



tions would be entirely changed in a few centuries. 
If the two stars spoken of as the " Pointers" in 
the Great Dipper had a proper motion as high as 
ten seconds a year this famous constellation would 
lose its distinctive shape in considerably less than 
a thousand years. 

Many stars have a common drift through space, 
but it is very rare for all the chief stars of a con- 
stellation to share the same direction of motion. 
Of the seven stars that form the outline of the 
Great Dipper five are moving in the same direc- 
tion, but the brighter star of the Pointers and the 
star at the end of the handle are moving in an 
entirely different direction. 

In the short time that has elapsed since its dis- 
covery determinations of the parallax, radial ve- 
locity and type of spectrum of the new star have 
yielded some interesting results. As seen in the 
36-inch Lick refractor it is a faint, orange-colored 
star of the 10y 2 magnitude, and it has the type 
of spectrum that is characteristic of stars far ad- 
vanced in evolution. It is what is known as a 
"dwarf" star of the type M. The variable star 
Alpha Herculis is a "giant" of the same class. 
The spectra of stars of type M are strangely fluted 
272 



SPLENDORS OF THE SKY 



in appearance, because of the presence of titanium 
oxide. It is not known as yet why stars of this 
type show spectra so dominated by this one sub- 
stance. 

The shifting of the lines of this star's spectrum 
toward the blue indicates that it is approaching 
the solar system, and measurements of the amount 
of this shift indicate a rate of approach in the 
line of sight of about sixty miles a second. It is 
a well known fact that if a star is receding from 
the earth the lines of its spectrum shift toward the 
red end of the spectrum and if it is approaching 
they shift toward the blue. So it is by the meas- 
urement of the lines in this star's spectrum that we 
can tell it is coming toward us at the rate of sixty 
miles a second. 

Some determinations of the parallax of this star 
have been made, and apparently it is the largest 
known, with the exception of the parallax of Alpha 
Centauri, the nearest star. In other words, Bar- 
nard's new star is probably our second nearest 
neighbor, and, its brightness is found to be five 
ten-thousandths that of the sun, which makes it 
one of the faintest stars so far known. 

It seems to be characteristic of "dwarf" stars 
273 



SPLENDORS OF THE SKY 



of this type to have high velocities. There is a 
decided tendency for stars to increase the speed of 
their journey through space as they increase in 
age, although such a velocity as this star possesses 
is far above what we should expect of a star of 
its class. It seems to be a true runaway star. 
Since faint stars have not yet received as careful 
scrutiny as has been given to the brighter members 
of the stellar system, possibly we may find in time 
that there are faint stars nearing extinction that 
travel through space with a velocity far exceeding 
any to which we have been accustomed. 

It is a peculiar fact that nearly all types of 
stars show a tendency to crowd toward the plane 
of the Milky "Way. Type M, to which the newly 
discovered star belongs, is a noted exception to 
this rule. Stars of this type show a spherical dis- 
tribution of space and are just as likely to be 
found at the poles of the Milky Way as in its 
plane. It has been suggested that dwarfs of this 
type with extremely high velocities such as Bar- 
nard's star possesses may have acquired their enor- 
mous speed while falling in toward the plane of 
the Milky Way from great distances without. 

Runaway stars have also been spoken of as 
274 



SPLENDORS OF THE SKY 



visitors passing through our stellar system from 
regions beyond. It has been said on good authority 
that there is not sufficient matter in our stellar 
system to control the motion of such a runaway 
star as G-roombridge, 1830. 

In the short time that has elapsed since the 
detection of the enormous proper motion of the 
new star some very interesting facts have been 
well established. This star is in all probability our 
second nearest neighbor at a distance of about six 
light years. Its luminosity is five ten-thousandths 
of the sun, making it one of the least luminous of 
all stars so far discovered, and it is, as we would 
expect, a star of most advanced type, bordering 
close upon extinction. 



275 



CHAPTER XXXVI 

MEASURING STAR DISTANCES 

^T^HE parallax of a star is its apparent displace- 
*■ ment in the sky due to the change in the 
earth's position in its orbit. It is the angle that 
93,000,000 miles, the distance from the earth to 
the sun, subtends at the star. Viewed from the 
vast majority of the stars this base-line shrinks 
to an immeasurable point. 

The direct measurement of the parallax of the 
stars by the triangulation method, by which the 
star's displacement at different times of year is 
determined either photographically or visually 
with reference to faint stars so distant as to have 
zero parallax, is possible only for a few stars near 
the solar system. The distances of nearly a thou- 
sand stars have been determined with more or less 
accuracy by this method. 
276 



SPLENDORS OF THE SKY 



The astronomer is here attacking a problem 
simple in principle but possessing great practical 
difficulties due to the minuteness of the angle to 
be measured. The largest known parallax, which, 
of course, belongs to the nearest star, is only sev- 
enty-eight hundredths of a second. This value of 
the parallax corresponds to a distance of about 
twenty-five trillion miles from the earth. 

Since to express the distance of the stars in 
miles would be as cumbersome and meaningless 
as to express the distance from the earth to the 
moon or neighboring planets in inches, a new unit 
for the measurement of stellar distances has been 
found in the velocity of light. In one second light 
travels 186,000 miles , in one year it travels nearly 
six trillion miles. The distance light travels in one 
year is spoken of as the light year. The distance 
of over twenty-five trillion miles that separates 
us from the nearest star is equal to four and one- 
third light years, and the rays of light leaving this 
star take four and one-third years to reach the 
earth. 

There are about twenty stars with parallaxes 
exceeding 0."2. A parallax of 0."2 corresponds to 
a little over sixteen light years. There are about 
277 



SPLENDORS OF THE SKY 



twenty stars known to be within this distance of 
the sun, and their distances have been determined 
by direct measurement of their parallaxes with an 
error that is less than 25 per cent, of the quantity 
measured. 

A directly measured parallax of ".02 has very 
little value, because unavoidable errors of in- 
struments may be nearly as large as the quantity 
to be measured. This parallax corresponds to a dis- 
tance of about 160 light years, and the tremendous 
extent of the universe can be judged from the 
fact that scarcely one hundred stars have paral- 
laxes greater than ".02. It is safe to say that no 
reliable measures of the distances of the stars 
lying beyond this point can be made by direct 
measurements of their parallaxes. 

The triangulation method is long and tedious 
and care must be taken to avoid systematic as 
well as accidental errors. The finally determined 
parallaxes are usually the result of a large number 
of independent measurements. 

There are a number of indirect methods of find- 
ing the parallax of the more distant stars. The 
most important of these is probably the one that 
deals with the proper motions of the stars. The 
278 



SPLENDORS OF THE SKY 



stars are all moving in various directions and at 
different rates. The actual motion or space motion 
of a star, as it is called, can be divided into two 
components. One is the motion in the line of 
sight toward or from the observer. This is called 
the radial velocity and can be determined by means 
of the spectroscope. The other component, the 
angular motion across the line of sight, is called 
the proper motion of the star. In general the 
nearer a star is to the earth the greater will be its 
proper motion. 

While parallax is a displacement in a star's 
position due to a change in the observer's posi- 
tion as the earth moves around the sun, proper 
motion is the displacement in the star's position 
due to its own motion across the line of sight, 
and, of course, the nearer the star is to the observer 
the more it appears to be displaced and the greater 
its proper motion. A star that has no measurable 
proper motion is at great distance from the earth. 

When both the radial velocity and the proper 
motion of a star are known its distance from the 
earth can be determined, for its cross-motion then 
becomes known both in angular measure and miles 
per second. Moreover, the distances of moving 
279 



SPLENDORS OF THE SKY 



groups of stars or moving star clusters can be 
found when the radial velocity of any one star in 
the group is known, since the stars are all moving 
at the same rate in the same direction. The extent 
of the group, in light years, the distances sepa- 
rating individual stars, as well as the distance of 
the group from the earth, become known as soon 
as the common proper motion of the stars and the 
radial velocity of one of the group has been 
determined. 

When the distance of a star is known, its abso- 
lute magnitude or luminosity, compared with the 
sun's luminosity, can also be found from a simple 
relation between the parallax and the apparent 
and actual brightness of the star. 

Some important results arising from investiga- 
tions of the proper motions and radial velocities of 
stars have been the discovery of star drift or star 
streaming, and the direction and amount of the 
sun 's motion through space as well as actual de- 
termination of distances in light years for indi- 
vidual types or groups of stars such as the Cepheid 
variables, the Orion stars, the giant red stars, the 
Pleiades, the Ursa Major group, and others. 

The motion of the sun through space also fur- 
280 



SPLENDORS OF THE SKY 



nishes a valuable base line for the determination 
of the distances of the stars. This motion amounts 
to nearly four hundred million miles a year and 
is, of course, increasing year by year. If the 
motion in one year gives too small a base line the 
motion in ten years or one hundred years can 
be used. In applying this method the individual 
motions of the stars have to be taken into account, 
but it is customary in computing the average dis- 
tance of a certain class of stars to go on the assump- 
tion that the sum of the individual motions of 
stars moving in all directions will compensate each 
other and the result will be the same as if all 
the stars were at rest. 

The average of the motions of a large number of 
stars across the line of sight will total zero and 
the average of their motions in the line of sight 
will be made up of their own motions plus the 
effect of the sun's motion, which is spoken of as 
the parallactic drift, since it is used to obtain the 
parallax of the group in question. When the sum 
of the radial velocities of all the stars in the 
group is formed the individual motions of the 
stars cancel each other and the value remaining 
represents the effect of the sun's motion on the 
281 



SPLENDORS OF THE SKY 

group. The amount and direction of the sun's 
motion is known and so the result gives directly the 
parallax of the group. 

Photometry, or the measurement of the apparent 
brightness of the stars, is becoming more and more 
important, since it has now become possible to 
find the absolute magnitude or light-giving power 
of stars of certain types independently of their 
distances. When both the absolute and apparent 
brightness of a star are known the star's distance 
can be found, just as when we know the candle 
power of a given light we can find the distance 
at which it will have a certain apparent bright- 
ness. 

Absolute magnitude is the new unit for measur- 
ing the light-giving power of suns, just as candle- 
power is the unit for measuring the light-giving 
power of terrestrial lights. It is defined as the 
apparent brightness a star would possess if it 
were at a distance of thirty-three light years from 
the earth, which is the distance that corresponds 
to a parallax of one-tenth of a second of arc. At 
this distance the sun, which has the value minus 
26.7 on the apparent brightness scale, has the 
value 5 in absolute magnitude. That is, if the 
282 



SPLENDORS OF THE SKY 



sun were thirty-three light years distant it would 
appear to be only a fifth magnitude star. 

The same scale of relative brightness holds for 
the absolute magnitudes of stars as for the ap- 
parent magnitudes, each unit of magnitude rep- 
resenting a change in intensity in the ratio of 
1 to 2y 2 . A change of five magnitudes means a 
change of a hundred fold in brightness. A star 
whose absolute magnitude is ten has only one- 
hundredth of the light-giving power of the sun, 
but if the absolute magnitude is zero the star is 
a hundred times brighter than the sun. An ab- 
solute magnitude of minus five means the object is 
10,000 times more brilliant intrinsically than the 
sun. It has been found that there is as great a 
range in the actual or absolute magnitudes of the 
stars as there is in their apparent magnitudes. 

We come now to a most important point, upon 
which depends the value of the photometric method 
of finding the distances of star clusters thousands 
and even hundreds of thousands of light years 
distant. That is, there appears to be an upper 
limit to the light-giving power of suns, and, more- 
over, certain types of stars possess a nearly uniform 
luminosity, the various stars of the type differing 
283 



SPLENDORS OF THE SKY 



little among themselves in light-giving power. The 
brilliant helium stars are all massive stars averag- 
ing one hundred times brighter than the sun. The 
giant red stars are still more luminous. The 
Cepheid variables, valuable because the periods 
of their light variations depend on their luminosity 
so closely that their absolute magnitudes can be de- 
termined when their periods are known, are also 
giant stars. The Cepheids with periods less than 
a day average one hundred times brighter than the 
sun, while those of longest period are rarely sur- 
passed in brightness by other stars. 

These facts furnish a simple accurate method 
for finding the distances of the globular star 
clusters whose brightest stars are helium stars, 
giant red stars and Cepheid variables. Measuring 
the apparent brightness of the stars in various 
clusters and knowing the absolute magnitudes of 
these same stars, the distances of the globular 
clusters can be found more quickly and easily than 
the parallax of a star a hundred or so light years 
from the earth can be found by the triangulation 
method and with less error. The average absolute 
magnitudes for the various types appearing in 
clusters were obtained originally by the proper 
284 



SPLENDORS OF THE SKY 



motion or parallactic drift method, using stars of 
these types comparatively near. 

It has been found by this simple method that 
the globular clusters are the most distant celestial 
objects known, except possibly the spiral nebulae. 
The only limit set for the measurement of the dis- 
tances of those objects lies in the limit of visi- 
bility of the telescope used. There appears, how- 
ever, to be a thinning out of these objects beyond 
a distance of 200,000 light years, and it is possible 
that all the globular clusters in the visible universe 
are within the reach of telescopes now in use. The 
60-inch Mount "Wilson reflector shows stars down 
to the twentieth apparent magnitude. The most 
distant globular cluster, which represents the 
greatest distance man has so far measured, is 
200,000 light years distant and its brightest stars 
are of the seventeenth apparent magnitude. A 
margin of apparent brightness still remains for the 
measurement of clusters still more distant if they 
exist. 



285 



CHAPTER XXXVI 

LAYING STARS IN THE BALANCES 

>TpHE weighing of the heavenly bodies, the sun, 
■*■ the planets and the stars, appears a stupen- 
dous problem, beyond solution, and so in truth it 
was until Newton discovered that the law of gravi- 
tation is universal and reaches even to the stars. 

The same force that holds us to the earth holds 
the earth in its orbit and sways the components 
of a double star system. Every particle of matter 
in the universe attracts every other particle with 
a force proportional to the product of the masses 
and inversely proportional to the square of the 
distance between them. The greater the masses 
and the less the distance between them the stronger 
their attraction for each other. It is upon this 
principle that the weighing of celestial as well as 
terrestrial objects rests. 

286 



SPLENDORS OF THE SKY 



If an object were not subject to the attraction 
of neighboring masses it would travel forever in 
a straight line. It is the attraction of nearby 
objects that causes the path to deviate from a 
straight line, and the amount of the deviation is 
a measure of the attractive force of the disturbing 
body 

In travelling eighteen and a half miles in its 
orbit, the distance passed over in one second, the 
earth falls about one-ninth of an inch from a 
straight line in the direction of the sun, and this 
is a measure of the sun's attraction for the earth. 

The earth's attraction for an object at its sur- 
face has been determined from observation, and 
since it is also equal to the earth's mass divided by 
the square of its radius it is possible to find the 
mass of the earth in terms of some known mass at 
its surface. 

This has been done a number of times, but the 
experiment is a very delicate and troublesome one, 
since the attraction between bodies at the earth's 
surface is so small that it is measured with great 
difficulty. 

A large metal ball or a mountain of known 
mass is usually chosen, and its attraction for some 

287 



SPLENDORS OF THE SKY 



object near by at a measured distance is deter- 
mined observationally. This attraction is propor- 
tional, according to the law of gravitation, to the 
mass of the body, which is known in this case, 
divided by the square of its distance from the 
object attracted. 

Comparing this attraction of one known mass for 
another on the earth's surface with the attraction 
of the earth for objects at its surface the ratio of 
the earth 's mass to the known mass is obtained. It 
has been found in this way that the earth's weight 
is about five and a half times that of an equal 
volume of water. 

This also gives the earth's density, which is 
simply its mass divided by its volume, the standard 
of comparison being the density of water. 

Since the total weight of the earth averages 
much more than the weight of the earth's crust 
it is evident that the material near the earth's 
centre is much more compressed and heavier than 
at its surface, due to the tremendous pressure of 
the overlying strata of the earth. 

Knowing the weight of the earth and its distance 
from the sun, we are in a position to find the sun's 
mass in terms of the earth's mass. It follows from 
288 



SPLENDORS OF THE SKY 



the law of gravitation that the mass of a body 
with a satellite is proportional to the cube of the 
distance of the satellite divided by the square of 
the satellite's period of revolution. 

This will apply to the planet's revolution around 
the sun and that of the moon around the earth. 
So if we find the cube of the earth's distance from 
the sun and divide it by the square of the earth's 
period of revolution, three hundred and sixty- 
five and a quarter days, we have a number that 
is proportional to the mass of the sun. 

It comes out that this number is about three 
hundred and thirty thousand times larger than 
the number proportional to the earth's mass found 
by dividing the cube of the moon's distance from 
the earth by the square of its period of revolution 
around the earth, so it is concluded that the mass 
of the sun is three hundred and thirty thousand 
times as great as the mass of the earth. 

To find its density compared with the earth's 
density we simply divide its mass compared with 
the earth's by its volume compared with the earth's 
volume, and we find that has only one-quarter of 
the density of the earth or about one and a half 
times the density of water. The sun therefore 

289 



SPLENDORS OF THE SKY 

weighs only one and a half times as much as an 
equal bulk of water would weigh. 

Just as we have found the numbers proportional 
to the earth's mass and the sun's mass so we can 
find the numbers proportional to the masses of all 
the other planets attended by satellites simply by 
dividing, as before, the cube of the distance of the 
satellite from the planet by the square of its period 
of revolution around the planet. 

Both of these quantities, the distances and 
periods, can be determined from observations of 
the satellites. Comparing, then, the values for 
each planet with the number proportional to the 
sun's mass, the mass of every planet that has 
satellites is found in terms of the sun's mass and 
also of the earth's mass. The mass of Jupiter and 
also of Saturn has been found with great accuracy, 
as both of these planets have a large number of 
satellites. 

Mercury and Venus, on the other hand, are the 
most difficult to weigh, for they have no satellites. 
Their masses have been found by observing their 
attractions for comets and near-by planets which 
produce "perturbations" in the motions and posi- 
tions of the attracted bodies. These perturbations 
290 



SPLENDORS OF THE SKY 



are, according to the law of gravitation, propor- 
tional to the masses of the two bodies and inversely- 
proportional to the square of the distance between 
the bodies affected. 

The most difficult body to deal with in the solar 
system is the moon. The problem of two attracting 
bodies is easily solved mathematically, or even three 
bodies if one of them is comparatively very small 
or very remote, but in the case of the moon we 
have a satellite that is very large compared to its 
primary. 

As a result there is a problem of three attract- 
ing bodies, the sun, the earth and the moon, to 
consider. The laws controlling the motions of 
three bodies are as infallible as in the case of two 
bodies, but the changes in the relative motions and 
distances of the three bodies are so complex that 
it lies beyond the power of mathematics to solve 
the problem completely, and only approximations 
to the complete solution are possible. 

One method for obtaining the mass of the moon 
is to compare the tide-raising force of the sun 
with the tide-raising force of the moon. Another 
is to measure the apparent displacement of the 
sun in the heavens at half moon due to the fact 
291 



SPLENDORS OF THE SKY 

that it is the centre of gravity of the earth and 
moon that revolves around the sun under the laws 
of gravitation and not the centre of the earth. 

This centre of gravity lies, it has been found, 
within the earth's surface and 2,880 miles from 
its centre, and it follows as a result of this that 
the earth's mass must be eighty-one and a half 
times the moon's mass. 

Knowing the relative masses of the members of 
our own solar system, how can we find the masses 
of the stars ? In the case of single stars this cannot 
be done. All the stars are apparently moving 
through space in straight lines. Up to the present 
time no curvature in the paths of isolated stars has 
ever been observed. If we were able to trace back 
the orbits of the stars for some hundreds of thou- 
sands of years we might make some interesting dis- 
coveries concerning stellar motions; but so far as 
we know now the stars are travelling in streams 
or groups along parallel lines to and fro under 
the general attraction of the entire system of the 
stars, no star appreciably deflecting the motion 
of any other. 

There are, however, many stars that are not 
single but consist of two or three, rarely more, 
292 



SPLENDORS OF THE SKY 



components revolving around a common centre of 
gravity. These are known as binary or multiple 
stars, either visual or spectroscopic, and it is pos- 
sible to determine their combined mass in terms 
of the sun's mass provided the distance of the 
binary star from us is known. 

This is done in the same way that we compute 
the mass of a planet that has a satellite. The dis- 
tance of the companion star from its primary star 
is found by observation, also the period that the 
satellite requires to make a revolution around the 
primary star. Then by the same law of gravita- 
tion the cube of the distance of the satellite divided 
by the square of its period gives the combined 
mass of the star system in terms of the sun's mass. 

In case the centre of gravity of the system can 
be found observationally the comparative masses 
of the two stars become known also. Only the 
masses of the nearest stars can be determined, 
since the distance of the star system from the earth 
is needed to solve the problem. The masses of 
about ten or twelve stars have been determined by 
this method, and though it is rather unsafe to 
generalize from such a small number of stars the 
results seem to indicate, what there is reason to 
293 



SPLENDORS OF THE SKY 



suspect from other investigations of a different 
nature, that the masses of the stars average about 
the same as the mass of our own sun. 

To weigh the heavenly bodies is not a simple 
matter. Many observations and computations are 
necessary. Since the discovery of the universality 
of the law of gravitation astronomers have been 
working on the problem and improving results, and 
they are not yet at the point where they are satis- 
fied with their results in spite of the fact that the 
error in the value of the sun's mass is less than 
one per cent, of the value given. The task of im- 
proving the values of the masses and positions of 
the heavenly bodies falls upon the theoretical 
astronomer and is usually undertaken by the 
National observatories or under special grants to 
individuals fitted to cope with this arduous 
problem. 



294 



CHAPTER XXXVIII 



WONDERS OF ORION 



ORION, the most magnificent of all the con- 
stellations, is visible throughout the greater 
part of the night in winter. The three bright stars, 
evenly spaced in a straight line, that mark the 
warrior's belt and the four brilliant stars in the 
form of a huge quadrilateral that outline his body 
are the most distinctive stars of the constellation. 
They are among the first stars to shine forth after 
sunset, appearing higher and higher in the eastern 
sky on each successive evening. 

In addition to forming the most impressively 
beautiful of all the constellations, the stars of 
Orion, with the exception of Betelgeuse, the deep 
red star that marks the giant's right shoulder, all 
belong to a connected system of inconceivably great 
extent associated with one vast enveloping nebula. 
295 



SPLENDORS OF THE SKY 



The denser portion of this nebula is known as the 
" Great Nebula in Orion/ ' considered by many to 
be the most beautiful telescopic object in the 
heavens. It covers a square degree in the sky and 
is associated with the central star in the " sword 
of Orion, ' ' which is formed by a row of faint stars 
extending in a southerly direction below the belt. 

In the midst of the great nebula glows an ex- 
quisite little trapezium of stars, two of which are 
attended by extremely faint companions. It is 
known as the sextuple star, Theta Orionis. Not 
far away, connected with the central nebula by a 
faint nebulous extension, is the triple star Iota 
Orionis, and the entire constellation abounds in 
double and multiple stars, many of which are sur- 
rounded by nebulous haze. 

It is well known that the helium stars, the type 
to which the Orion stars belong, are not univer- 
sally distributed in space. They favor certain 
regions and occur in loosely formed groups or 
clusters, usually attended by nebulosity. They are 
the most massive and the hottest of all the stars, 
and they are never to be found far from the plane 
of the Milky Way. 

Prof. W. H. Pickering has made recent investi- 
296 



SPLENDORS OF THE SKY 



gations of the distance of the great Orion nebula, 
and the size and luminosity of the Orion stars. 
According to his results, this glorious constellation 
is constructed on a plan of inconceivable grandeur. 
The distance of the great Orion nebula he has 
found to be a little over sixteen hundred light 
years, corresponding to a parallax of ".002. If 
we desired to express this distance in miles 
we would have to multiply sixteen hundred by 
the value of one light year in miles, or 63,000 
times the distance from the earth to the sun, re- 
membering that the distance from the earth to the 
sun is 93,000,000 miles. According to this same 
estimate the luminosity of the brilliant blue-white 
star Rigel, the brightest star in the constellation, 
is nearly ninety thousand times that of our own 
sun, while the triple star Iota Orionis mentioned 
above is fifteen thousand times more luminous than 
our sun. 

Another estimate of the distance of the Orion 
nebula made recently by Kapteyn places it at a 
distance of six hundred light years, corresponding 
to a parallax of ".0054, and gives the light- 
giving power of Rigel as nearly twelve thou- 
sand times that of the sun and the light-giving 
297 



SPLENDORS OF THE SKY 



power of Iota as two thousand times that of the 
sun. If Prof. Pickering's estimate gives approxi- 
mately the true distance of this wonderful con- 
stellation then its brightest star Eigel is a super 
giant among the stars, unsurpassed in brilliancy 
by any other star unless we make an exception of 
giant Canopus, the magnificent star of the South- 
ern Hemisphere. 

Astronomers have long held the theory that the 
helium stars associated with the great irregular 
nebulas, such as the stars of Orion and the Pleiades, 
are being condensed from the nebulae with which 
they are associated. The order of evolution has 
always been assumed to be from nebula to star. In 
light of more recent knowledge the idea is grad- 
ually and persistently growing that in some in- 
stances the evolution may be progressing toward 
the nebula instead of away from it. In other 
words, the nebulosity surrounding the Pleiades and 
many of the stars of Orion may have been thrown 
off from the surfaces of these stars. In the solar 
corona and the zodiacal light and the tails of 
comets, it has been suggested, we may see in a 
slight degree the laws that govern the repulsion 
of matter, under light pressure and possibly elec- 
298 



SPLENDORS OF THE SKY 



tro-magnetic forces, at work in our own solar 
system. 

The characteristics of the novas or temporary- 
stars also give support to this view. Novae have 
been seen to change from helium type stars to 
bright line stars and then to planetary nebulae, 
exactly reversing the accepted order of develop- 
ment. 

In his discussion of the great nebula and helium 
stars in Orion Prof. Pickering says: "It was 
formerly universally supposed that the nebulae 
were condensing, but ... an appearance some- 
what similar to the nebula was produced by photo- 
graphing an explosion of flash powder." C. D. 
Perrine, writing in the Astro-physical Journal, 
says: "The dark, finely divided matter which is 
believed to exist in the distant galactic regions 
may be none other than condensed nebulosity; in 
place of the early Orion stars, for example, being 
wholly in the process of condensing from their 
inclosing nebulous envelope, this nebulosity is, in 
fact, largely the result of a great catastrophe, the 
nebulosity having been thrown off in the process." 
He asks : "Is this also true of the nebulosity in the 
Pleiades with the difference that in the Pleiades 

299 



SPLENDORS OF THE SKY 



the stars are slightly ' older' in type and the nebu- 
losity not self-luminous % Has this nebulosity 
frozen from a gaseous state?" 

It is possible, according to Perrine, that the 
Orion or helium type stars are extremely massive 
and hot and confined to certain regions as a result 
of varying external conditions existing in different 
parts of the universe. Where cosmic matter is 
dense stars of great mass and high temperature 
would be found. The energy obtained from the 
material gradually swept up by these stars would 
exceed the energy lost by radiation. Their mass 
and temperature would increase while light 
pressure and electro-magnetic forces would drive 
from these stars the lighter gases that form the 
nebulosity enveloping them. 

In parts of the universe where the cosmic matter, 
either meteoric or gaseous, is less plentiful, the 
evolution of the stars would be, on the contrary, 
away from the nebula and toward the later and 
cooler type stars, culminating in extinct, dark stars 
following after the dwarf red type stars in 
evolution. 



300 



CHAPTER XXXIX 

THE CONSTELLATIONS OF WINTER 

\ MONG the sparkling brilliants of midwinter 
«* *• skies are three, Betelgeuse in Orion, Sirius in 
Canis Major, the Greater Dog, and Procyon in 
Canis Minor, the Lesser Dog, that outline in the 
heavens a huge equilateral triangle that is as con- 
spicuous a figure in the winter as the Great Square 
in Pesagus is in early fall. 

During the early evening hours of February this 
massive triangle of first magnitude stars will be 
found not far from the meridian, the two Dog Stars 
following closely at the heels of the warrior Orion 
as with uplifted club he pursues Taurus, the Bull, 
across the heavens to the westward. 

Ruddy Betelgeuse is in the right shoulder of 
Orion, and not far away to the west glows Alde- 
baran, the brightest star in the V-shaped group of 
301 



SPLENDORS OF THE SKY 



the Hyades, also deeply red, representing the bale- 
ful light in the eye of the Bull as he charges with 
lowered head at the warrior Orion. 

At no other season is there presented so finely to 
view such an impressive assemblage of first magni- 
tude stars. Eight of the twenty brightest stars in 
the heavens are now visible in our latitudes in the 
early evening. 

If we are south of the thirtieth parallel we may 
also see Canopus of the Southern Hemisphere, sec- 
ond only to Sirius in apparent brightness, the star 
of immeasurable distance and unimaginable size 
and splendor that in actual luminosity makes Sir- 
ius appear but a dwarf. Ten thousand times the 
light-giving power of the sun is the lowest limit 
that can be set for the light-giving power of this 
supergiant, and it may far exceed this amount. 

Sirius, at the southeastern vertex of the tri- 
angle, is one of our nearest neighbors in space, and 
is only surpassed in brightness by the planets Jup- 
iter and Venus and occasionally Mars. Its light 
takes between eight and nine years to reach our 
solar system, however, and its distance, if we wish 
to express it in miles, amounts to about 550,000 
times the distance from the earth to the sun. 
302 



SPLENDORS OF THE SKY 



Sirius is attended by a companion that is one of 
the most feebly luminous bodies known. Though 
its mass is about one-half that of Sirius, it would 
take 20,000 such companions to equal Sirius in 
brightness. The two stars are separated from each 
other by a distance of 1,800,000,000 miles, which is 
the same as the distance of the planet Uranus from 
the sun. Though the light of the two stars com- 
bined is forty-eight times that of our own sun, 
their combined mass is only between three and 
four times the sun's mass, so low is their density. 
Procyon, at the northeastern vertex of the triangle, 
is another neighbor of the solar system, being only 
ten light years distant. It also is attended by a 
companion star. 

The two combined radiate about six times as 
much light as our own sun, but are only one and 
one-third times more massive. "Were our own sun 
as far from us as Procyon it would appear to be 
only one-sixth as bright as this first magnitude star. 
Buddy Betelgeuse, the third star in the triangle, 
presents a strong contrast to the other two in every 
way. 

It is in the first place so distant that it gives no 
measurable parallax. In comparison to Betel- 

303 



SPLENDORS OF THE SKY 



geuse, Sirius and Procyon are dwarfs. Like Eigel 
and Canopus, Betelgeuse is one of the supergiants 
of the universe. Though one of the stars in Orion 
it is not physically associated with the great con- 
stellation and its enveloping nebulosity. It is trav- 
elling in a different direction and simply chances 
to lie in such a position as to complete the quad- 
rangle that roughly outlines the form of the war- 
rior. 

Betelgeuse is not only far more distant and 
far more luminous than Sirius and Procyon, 
but also radically different in its physical con- 
dition. 

These three stars represent three distinctive 
types and three widely different stages of evolu- 
tion. Sirius is a star of the hydrogen type, which 
is, in fact, sometimes referred to as the Sirian type 
after this illustrious member. Next to the helium 
stars, of which nearby Rigel, the brightest star in 
Orion, is an example, these hydrogen stars are the 
hottest of all the stars. 

Their brilliant surfaces are not veiled by cooler 
enveloping layers of metallic vapors such as sur- 
round the photosphere of our own sun and stars 
still more advanced in type. Intense absorption 
304 



SPLENDORS OF THE SKY 



lines of hydrogen in the spectrum give them their 
characteristic name and prove that they are sur- 
rounded by glowing hydrogen gas. 

The intense blue-white and white light of the 
helium and hydrogen stars respectively is an in- 
dication of their great heat, for the hotter a body 
the more intense are its radiations in the violet and 
ultra violet end of the spectrum. 

As a body cools the maximum intensity of its 
radiations -shifts toward the red end of the spec- 
trum. 

Fully half of all the stars so far examined have 
proved to be either helium or hydrogen stars. This 
may be due to the fact that these intensely brilliant 
stars may be seen to a far greater distance than 
less luminous stars. 

Procyon stands between the hydrogen and solar 
stars in type, and more closely approaches our 
own sun in its physical condition. Strong lines 
of calcium are one of the most distinctive features 
of the spectra of such stars, though the hydrogen 
lines are still very conspicuous, as they are also in 
the spectrum of our own sun. 

Stars such as Procyon are usually spoken of as 
calcium stars, owing to the prominence of the lines 
305 



SPLENDORS OF THE SKY 



of this element in their spectra. Other metallic 
lines also begin to appear faintly at this stage of 
evolution and such stars are slightly tinged with 
yellow as their atmospheres become charged with 
the vapors of the denser gases. 

Compared to Sirius, Procyon is noticeably yel- 
lowish and this tinge is still further deepened in 
the solar stars to which our own sun belongs. Bril- 
liant Capella, also visible at this time, due north of 
Betelgeuse and midway between it and the pole, is 
a typical solar type star in which the metallic lines 
so faint in Procyon have increased in strength 
until they equal the hydrogen lines in intensity. 
Such stars are decidedly cooler than the hydrogen 
and helium stars and the more deeply they are 
tinged with yellow the more are their atmospheres 
charged with the heavier metallic vapors. 

A still later stage in the evolution of the stars is 
typified in the orange-colored star Aldebaran in 
the Hyades just to the northwest of Orion. In 
stars of this class the metallic lines have increased 
in strength until they have become stronger than 
the lines of hydrogen. The rays from the blue end 
of the spectrum have become absorbed more and 
more in an increasingly dense atmosphere and for 
306 



SPLENDORS OF THE SKY 



this reason such stars are reddish orange in ap- 
pearance. 

We now arrive after all these gradual changes 
at the type of the giant red star Betelgeuse that is 
so radically different from the types of the two 
stars Sirius and Procyon. Betelgeuse is an irregu- 
larly variable red star. 

The majority of stars of this class are variable 
in their radiations for some reason not clearly un- 
derstood. Any one observing this interesting red 
star from season to season will readily note its pe- 
culiar fluctuations of brightness. 

At times it is only a shade brighter than Alde- 
baran, a convenient star with which to compare it. 
Again it will be equal in brightness to Rigel, 
diagonally opposite to it in the quadrilateral of 
stars. 

The spectrum of Betelgeuse is that of a typical 
giant "M" star, as it is called astronomically. It 
is beautifully fluted in appearance, due to the pres- 
ence of the compound known as titanium oxide. 
The presence of oxides in the atmosphere of a star 
indicates a decided drop of temperature, for no 
such compounds could exist unless the temperature 
were comparatively low. Why titanium oxide 
307 



SPLENDORS OF THE SKY 



should so completely dominate the spectra of such 
stars is one of the unsolved mysteries of the stars. 
It is also one of the compounds that appear in the 
spectra of the sun spots. The temperature of sun 
spots, it is well known, is decidedly below that of 
the surrounding solar surface. Only a few hundred 
stars of the same type as Betelgeuse are known and 
they are all believed to be at great distances and 
at least several thousand times more luminous than 
our own sun. 

The cause of the irregular fluctuations of bright- 
ness of these stars is believed to lie within the 
stars themselves. No law or order in its workings 
can be detected as yet, however. Betelgeuse usually 
goes through its irregular variations of light, which 
amount to about half a magnitude at most, within 
a year or two. 

There is, at the greatest, a change of more than 
forty per cent, in the intensity of the radiations 
of this star. Its sudden and unexpected increases 
of luminosity may possibly occur when its dense 
atmosphere of metallic vapors is temporarily 
rent by the pressure of pent-up forces within 
a highly heated interior. To live upon planets 
encircling such suns would appear to us extremely 
308 



SPLENDORS OF THE SKY 



hazardous and no more to be relished than exist- 
ence near an active volcano. 

An outburst of activity that would rapidly 
change the intensity of the radiations of such a 
star nearly fifty per cent, would have a most dis- 
astrous effect upon organisms with which we are 
familiar. And yet adaptations to conditions under 
the sway of such an erratic ruler might be such 
that the life process would continue there no more 
disturbed than it is on our own planet when pass- 
ing clouds temporarily conceal the face of the 
sun. 



309 



CHAPTER XL 

THE CONSTELLATIONS OP SPRING 

TT IS not difficult to locate all the constellations 
*■ for a certain season of the year if we once fix in 
our minds the positions of two or three of the 
more prominent groups. Let us consider first the 
two constellations known as Ursa Major, "The 
Great Bear, ' ' and Leo, l ' The Lion. ' ' Both are con- 
spicuous in the spring, and we should have no 
trouble in locating them readily. 

At nine o'clock on the first of April these two 
groups are almost directly on the meridian. A 
month later they, as well as all the other constel- 
lations, have apparently shifted about thirty de- 
grees westward. The winter constellations have 
disappeared below the western horizon and the con- 
stellations that are overhead in summer evenings 
are now appearing on the eastern horizon. Taking 
310 



SPLENDORS OF THE SKY 



as our time of observation May first, about nine 
o'clock in the evening, we find in the north, just 
west of the meridian, the seven stars of the Big 
Dipper, or Great Bear, and south of it Leo facing 
westward. 

The head of Leo is outlined by a sickle-shaped 
group of stars, six in all, with the bright, white star 
Kegulus in the end of the handle. To the eastward 
we see the other stars that outline the body. Dene- 
bola, a star of the second magnitude, marks the 
tail and is about twenty-five degrees east of Regu- 
lus. "With these reference points we can easily lo- 
cate other conspicuous constellations. Southeast 
of Leo is Virgo, a large Y-shaped constellation, 
which contains the beautiful white star Spica, and 
again southeast from Virgo is the small constella- 
tion Libra, marked by four rather faint stars. To 
the southwest of Spica is a more conspicuous group 
of stars of the second and third magnitude in the 
form of a quadrilateral. This is the constellation 
Corvus, and just west of Corvus is the less conspic- 
uous group known as Crater. In the southern skies 
we also have the long constellation of Hydra, which 
extends from a point a little southwest of Eegulus, 
where a small group of faint stars mark the head, 
311 



SPLENDORS OF THE SKY 



to a point in the southeast, where the fiery Antares 
will soon rise in the constellation Scorpio. Hydra 
contains one second magnitude star known as Al- 
phard or Cor Hydrae, standing very much alone. 
It is about twenty degrees south of Eegulus and a 
little to the westward. This long, but rather faint 
constellation of Hydra extends nearly ninety de- 
grees across the southern sky below Leo, Virgo, 
Crater, Corvus and Libra. Let us return now to 
the Great Bear, which, by the way, is a much more 
extensive constellation than the part which forms 
the Big Dipper, or the tail and body of Ursa Major. 
A considerable portion of the space south and east 
of the configuration known as the Big Dipper be- 
longs to Ursa Major. It is occupied, however, by 
inconspicuous stars. On a line between the end 
star in the handle of the Dipper and Denebola in 
Leo are situated two very interesting, though small, 
constellations; Canes Venatici, the more northerly 
one, is marked by two stars, the Hunting Dogs, 
with which Bootes the Herdsman is chasing the 
Great Bear around the pole. The northern of the 
two dogs is Asterion, the southern Chara. Be- 
tween Denebola and Canes Venatici is the constel- 
lation, almost directly overhead at this time, known 
312 



SPLENDORS OF THE SKY 



as Coma Berenices. In this constellation, it is esti- 
mated, over a hundred nebulaa are gathered in 
a space no greater than that covered by the full 
moon. This little constellation also contains a 
great number of fifth and sixth magnitude stars 
and many interesting doubles. Canes Venat- 
ici also contains some fine doubles and a beautiful 
star cluster, as well as the noted "Whirlpool Neb- 
ula. ' ' Both constellations offer a fine field for the 
telescope. 

If we now turn to the western sky we can 
trace out a bright arc of first and second mag- 
nitude stars beginning with Capella, the yel- 
lowish star in the northwest in the constella- 
tion Auriga. We can distinguish Capella also 
by the group of three stars about iive degrees 
to the southwest, known as the "Kids." Fol- 
lowing this arc from Capella southward we come 
first to Beta Auriga?, then in order, Castor and 
Pollux in Gemini and finally Procyon in Canis 
Minor. 

In the east we now see the large constellation 

of Hercules. Hercules contains no star of the first 

or second magnitude, but many of the third. It 

contains one of the finest star clusters in the heav- 

313 



SPLENDORS OF THE SKY 



ens, seen on a clear, dark night as a patch of 
white light. The telescope dissolves it into a 
magnificent cluster of over 5,000 stars. Northeast 
of Virgo and southeast of Ursa Major is the large 
constellation of Bootes, a kite-shaped configuration 
of stars whose principal star is the ruddy Arcturus. 
Almost overhead now is the conspicuous equilateral 
triangle formed by the three bright stars, Dene- 
bola in Leo, Spica in Virgo and Arcturus in Bootes. 
Once located in the heavens it will never be forgot- 
ten, and when we see it high in the heavens in the 
evening we know that spring has come once more, 
for it is known as the characteristic configuration 
of spring. Between Hercules and Bootes is the 
Northern Cross, a beautiful little semicircle of six 
small stars. It was in this constellation that the 
" blaze star," or Nova, of 1866 appeared. In the 
northeast is the small constellation of Lyra, iden- 
tified at once by the brilliant blue- white star Vega. 
Directly east of Vega is the constellation Cygnus, 
known as the Northern Cross, now coming into 
view low in the northeast. 

Bootes, Corona Borealis, Hercules, Lyra and Cyg- 
nus are all in a line across the heavens and Arc- 



314 



SPLENDORS OF THE SKY 



turns, in Bootes, Alphacca, the brightest star in 
Corona; Vega in Lyra and Deneb in Cygnus are 
on a diagonal line directed toward the north- 
east. 



315 



CHAPTER XLI 

THE CONSTELLATIONS OP SUMMER 

THE constellations that are most noticeable 
during the summer months are Scorpio in the 
south, Hercules and Corona Borealis directly over- 
head at nine o 'clock the middle of July and Ophiu- 
chus and Serpens between these two constellations 
and Scorpio. 

In the northwest can be seen the Big Dipper, 
which never sets in our latitudes, but is best seen 
in the spring and summer months. In the fall and 
winter it appears to rest upon the horizon and is 
too low to be well seen. The head of Draco is now 
nearly on the meridian and just north of Hercu- 
les. It is marked by a group of four fairly bright 
stars, and from there the neck and body can be 
traced first eastward, then curving northward and 
bending sharply westward, so that the body lies 
316 



SPLENDORS OF THE SKY 



between the creature's head and the Little Dipper, 
and twines around between the two Dippers. The 
tip of the tail lies at the middle of the line between 
the Pointers and the Pole Star. The Pointers, we 
remember, are the two stars farthest from the 
handle of the Big Dipper that outline the outer 
edge and a line drawn through them and extended 
northward a distance about equal to the whole 
length of the Big Dipper brings us to the Pole 
Star, which is a second magnitude star at the end 
of the handle of the Little Dipper. 

The Northern Cross, in Cygnus, is now conspic- 
uous in the northeast. The brightest star, Deneb, 
or Arided, as it is better called, for there are sev- 
eral Denebs in different constellations, is situated 
at the northern end, or top, of the Cross and Albireo, 
the noted double at the bottom. Arided, or Deneb, 
lies in a line with Vega in Lyra, the next constella- 
tion west of Cygnus, Alphacca in Corona and Arc- 
turus in Bootes, which is now west of the meridian. 

Spica, in Virgo, sparkles brilliantly, low in the 
southwest. Vega still remains the most brilliant 
star visible, although ruddy Arcturus is of the same 
magnitude. "We include in our list of bright 
stars Antares in Scorpio, which is on the meridian 
317 



SPLENDORS OF THE SKY 



well to the southward at this time, and Altair, in 
Aquila, a yellow star of the first magnitude, which 
is well up in the eastern sky. It is readily found 
from the fact that it is attended by two fainter 
stars exactly in line with it and at nearly equal 
distances on either side. In the constellation of 
Aquila, about twenty degrees southwest of Altair, 
appeared the brilliant Nova of 1918, known as Nova 
Aquilae No. 3, since it was the third Nova to ap- 
pear in this constellation. About fifteen degrees 
northeast of Aquila is the little diamond-shaped 
group of third magnitude stars, known as Del- 
phinus and often called "Job's coffin.' ' 

Vega, as well as Altair, is accompanied by two 
fainter stars. They form a small equilateral tri- 
angle with it, whose sides are only two and one- 
half degrees long. A sahrp eye will detect the fact 
that Epsilon Lyrae, the northernmost of the two 
stars, is double, and a small telescope will show that 
the star is really quadruple, each of the two com- 
ponents of the wide double being also double. It is 
the finest example we have of a quadruple star. 
All four stars are physically connected and form 
one mighty system. Beta Lyra?, which lies about 
eight degrees southeast of Vega, is both a variable 
318 



SPLENDORS OF THE SKY 



and double star. In the short period of thirteen 
days its brightness fluctuates nearly a magnitude. 
Its change in brightness is due to the fact that it 
has a companion star that intercepts at times part 
of the light from the brighter star. 

It requires considerable stretch of imagination 
to trace some of the mythical and legendary figures 
that have been mapped out in the heavens. It is 
rather difficult to see that Lyra is a harp or Her- 
cules and Ophiuchus heroes performing wonder- 
ful feats with serpents. Bootes is a hunter pur- 
suing the Great Bear around the Pole, accompan- 
ied by the two hounds, Canes Venatici, though ac- 
cording to some legends he is represented as a 
herdsman driving the seven plough oxen, the stars 
that form the Big Dipper. The giant Hercules 
stands with his foot on the head of Draco and his 
body is marked by a quadrilateral of four stars 
midway between Lyra and Corona Borealis, or the 
Northern Crown. The latter constellation is one 
of the few that really resembles the object for 
which it is named, as it consists of a nearly perfect 
semicircle of six stars. The brightest, Gamma or 
Alphacca, is the gem in the crown. 

Alpha Hercules, which marks the head of Her- 
319 



SPLENDORS OF THE SKY 



cules, is a variable star which, changes irregularly 
in brightness from the third to the fourth magni- 
tude. It is also a beautiful orange and blue double. 
One can easily find it in connection with Alpha 
Ophiuchi, which is about six degrees east of it and 
which forms with Vega and Altair a nearly equi- 
lateral triangle. Alpha Hercules is the fainter of 
the two stars. The large constellations of Ophiu- 
chus and Serpens lie west of Aquila and south of 
Hercules and Corona. The head of Serpens 
lies about ten degrees south of Corona Borealis and 
is marked by a group of small stars ; from there a 
line of bright stars can be traced first to the south- 
west for a few degrees, then south and eastward 
almost to Aquila. Ophiuchus, the serpent bearer, 
is another mythological figure represented by a con- 
siderable number of fairly bright stars grouped in 
rather indefinite forms. The hero is represented 
with his feet on Scorpio and his head very close to 
Hercules, while he grasps Serpens with both hands. 
Scorpio is directly south of Ophiuchus. Fiery An- 
tares marks the creature's heart and his tail is a 
long line of stars reaching nearly to the southern 
horizon. The constellation is of peculiar shape and 
easily recognized. The two bright stars in Libra, 
320 



SPLENDORS OF THE SKY 



the next constellation westward, marked the crea- 
ture's claws according to some ancient maps, but 
there is considerable confusion as to the exact 
boundary between the two constellations. Antares 
is a most interesting object in the telescope, as it is 
a double star with a small green companion. As 
its name indicates it is the ' ' Rival of Mars ' ' and to 
the naked eye shows a strong resemblance to the 
ruddy planet. 

Sagittarius is now visible in the southeast, 
its little inverted milk dipper outlined by five stars. 
A little southwest of the star in the end of the 
handle is a small triangle of stars, making a no- 
ticeable group of eight stars in all. Sagittarius 
and Scorpio mark one of the most interesting re- 
gions of the sky, as the Milky Way is particularly 
dense and bright here, and very peculiar in struc- 
ture. According to the most recent researches it is 
in this general direction that the center of the 
sidereal universe is located. 



321 



CHAPTER XLII 

THE CONSTELLATIONS OF AUTUMN 

Tp ACH season of the year brings its character- 
■*-' istic configuration of stars in the heavens. 
The magnificent constellation of Orion is always 
associated with winter months. The great triangle 
formed by Spica, Denebola and Arcturas appears 
in spring and early summer, while the Scorpion 
with red Antares glowing in its heart is seen in 
southern skies on midsummer nights. In Autumn 
we have the Great Square in Pegasus, visible in the 
east in September, overhead in October. 

At nine o'clock the middle of September the 
Northern Cross of the constellation Cygnus is di- 
rectly in the zenith, while Altair in Aquila is just 
west of the meridian. Altair can always be recog- 
nized by the two fainter stars that are in line with 
it at nearly equal distances on either side. Del- 
322 



SPLENDORS OF THE SKY 



phinus, the Dolphin, is a little diamond-shaped 
group of third magnitude stars commonly spoken 
of as Job's Coffin, that now can be found on the 
meridian south of Cygnus and about twenty de- 
grees to the northeast of Altair. It contains a few 
other faint stars visible to the naked eye, in addi- 
tion to those that form the diamond. Vega in 
Lyra is the most brilliant star visible and is just 
west of the meridian. 

In western skies the extensive constellation of 
Hercules is still in view and south of it Ophiuchus 
and Serpens. Bootes and Scorpio are now at the 
western horizon and the Dipper is far over to the 
northwest. 

Turning to the eastern half of the heavens, we 
cannot fail to discover the Great Square in Pe- 
gasus. It is best considered in connection with 
Andromeda, as the star in the northeast corner of 
the square does not belong to the constellation 
Pegasus, but is Alpha Andromedse, one of the three 
stars in a curved line that belong to the constel- 
lation Andromeda, which is now in the northeast 
just south of the peculiar W-shaped group of stars 
that forms the constellation of Cassiopeia. An 
imaginary line drawn from Polaris, the Pole Star, 
323 



SPLENDORS OF THE SKY 



through the star in the W that is farthest west, 
known as Beta Cassiopeise, and extended as far 
again, brings us to Alpha Andromedaa in the corner 
of the Great Square. About fifteen degrees due 
west is Beta Pegasi, an irregularly variable star 
that marks the northwestern corner of the square. 
Near this star is a group of three fainter stars that 
also belong to the constellation Pegasus. The star 
that marks the southwestern corner is about fifteen 
degrees due south of Beta Pegasi, and is known as 
Markab. A line from Alpha Andromedae drawn 
diagonally across the square to this star and ex- 
tended as far again passes through the neck and 
head of the Winged Horse. His hindquarters are 
missing on star maps that show the mythological 
figures, but his forelegs are marked by four faint 
stars northwest of the square and just east of Cyg- 
nus. About fifteen degrees due south of Alpha 
Andromedas is the second magnitude star that com- 
pletes the Great Square. The entire constellation 
of Pegasus covers an extensive region in this por- 
tion of the heavens. 

The Great Nebula in Andromeda, visible even to 
the naked eye, can be found about ten degrees 
northwest of the middle star in the line of three 
324 



SPLENDORS OF THE SKY 



stars that characterizes the constellation of Andro- 
meda. It forms a little triangle with two faint 
stars near it. 

Just east of the meridian at this time and above 
and west of the W-shaped group of stars in Cas- 
siopeia is the constellation Cepheus, which con- 
tains very few bright stars. The remarkable va- 
riable star Delta Cephei, which changes more than 
a magnitude in brightness in about five days, is 
one of the stars in a little triangle that marks the 
king's head. Cepheus is represented as sitting 
behind his wife, Cassiopeia, with his feet on the 
tail of the Little Bear. Andromeda, the daughter, 
is represented with her head resting upon the 
shoulder of Pegasus, the winged horse, that brought 
Perseus to rescue her from Cetus, the sea monster, 
lying far to the south beyond the constellations 
Aries and Pisces. Perseus is the brilliant constel- 
lation just east of Andromeda crossed by the Milky 
Way. 

The Milky Way is now a beautiful sight upon 
clear nights. It passes from Cassiopeia across the 
shoulder of Cepheus, through Cygnus in the zenith 
and thence divides into two branches, one passing 
through Aquila and Sagittarius, and the other 
325 



SPLENDORS OF THE S'KY 



through Ophinchus to Scorpio. Near this point 
the two branches again meet. 

Of the zodiacal constellations now visible Sagit- 
tarius is readily found in the southwest by its 
peculiar configuration of eight bright stars, 
five in the shape of a little dipper inverted toward 
the southern horizon and three forming a tri- 
angle southwest from the star at the end of the 
handle. 

East of Sagittarius come in order the three 
zodiacal constellations, Capricornus, Aquarius, and 
Pisces. Capricornus, the sea goat, represented with 
the head and body of a goat and tail of a fish, has 
few bright stars. It contains, however, one of the 
few double stars visible to the naked eye, Alpha 
Capricorni. 

A line drawn from Albireo at the bottom of the 
northern cross through Altair and extended about 
as far again, brings us to this double. Three 
degrees further south is Beta Capricorni, the 
brightest star in the constellation. 

Aquarius, the water bearer, is east and north of 
Capricornus and southwest of Pegasus. The char- 
acteristic configuration of this constellation is the 
little Y of third and fourth magnitude stars about 
326 



SPLENDORS OF THE SKY 



20 degrees southwest of the square In Pegasus. 
This is supposed to represent the water jar from 
which Aquarius pours the stream of water out- 
lined by many faint stars lying to the southwest 
and south. At the southern end of this stream is 
Piscis Austrinus, the Southern Fish, which eon- 
tains one first magnitude star, Fomalhaut, just 
visible above the southern horizon at this time of 
year. It is in line with the western edge of the 
square in Pegasus, but fully 45 degrees south. 
Directly south of the Great Square in Pegasus is a 
little polygon of faint stars which marks the head 
of one of the two fish in the zodiacal constellation 
Pisces. A line of faint stars runs from here east- 
ward to meet another line of stars extending in a 
northerly direction toward the constellation And- 
romeda. This second line of stars represents the 
second fish in the constellation, and contains no 
bright stars. Part of the large constellation of 
Cetus, the Whale, is directly south of Pisces 
and Beta Ceti, which stands entirely alone, is 
the brightest star in this part of the heavens. 
The Chaldeans called this region the Sea, and 
it is not strange, for we have here Cetus, the 
Whale, the two fish in Pisces and Pisces Aus- 

327 



SPLENDORS OF THE SKY 



trinus, the Southern Fish, as well as Aquarius, 
the Water Bearer, Capricornus, the Sea Goat, and 
Delphinus, the Dolphin, quite an aquatic collec- 
tion! 



328 



CHAPTER XLIII 

BRILLIANT STARS OF THE SOUTHERN HEMISPHERE 

Q TAR gazers of northern lands often overlook 
^ the fact that some of the most brilliant and 
beautiful stars and finest nebulae and star clusters 
in the heavens belong to the southern hemisphere 
and are not visible in our latitudes. 

The brilliant first magnitude star Formalhaut 
that culminates in the zenith in thirty degrees 
south latitude comes about twenty degrees above 
our southern horizon in late summer and autumn 
months to give us a hint of the beauties of the 
southland, and if our view of the southern horizon 
is not obstructed by houses, trees or mountains, as 
is so often the case, we may then see this interest- 
ing star of the south. Stars are never seen at their 
best when near the horizon, however, for we then 
view them through denser layers of atmosphere 
329 



SPLENDORS OF THE SKY 



than if they were nearer the zenith. All ce- 
lestial bodies shine brightest when they are over- 
head. 

Magnificent blue-white Canopus, the second 
brightest star in the heavens, lies just below our 
southern horizon in the large and important south- 
ern constellation of Argo Navis, named for the fa- 
mous ship of the Argonauts. It is usually divided 
into three constellations — Puppis, Carina and Vela. 
Canopus was the chief pilot of the Argonauts, but 
the star was known and worshipped on the banks 
of the Nile long before it received its name from 
the Greeks and it has been called the Star of Egypt. 
It has also been a guide to many tribes in Africa, 
South America and Australia in their journeys 
through pathless wilds. 

Although Sirius appears nearly twice as brilliant 
as Canopus, this is due only to the fact that Sirius 
is comparatively near to us, not quite nine light 
years distant, while no accurate measurement of 
the distance of Canopus has yet been made. It is, 
as far as we know, the greatest of all the giant 
suns and its light-giving power has been estimated 
as high as fifty thousand times that of our own 
sun. Sirius, with a brilliancy estimated at forty- 
330 



SPLENDORS OF THE SKY 



eight times that of the sun, shrinks into a pygmy 
when compared with Canopus. 

Other brilliant first magnitude stars in southern 
skies that are invisible to us are Alpha Centauri, 
the nearest of all the stars and one of the finest 
doubles in the heavens; Beta Centauri, a beautiful 
white star near Alpha — the two reminding us of 
the twins in Gemini; Achernar, far south in the 
river Eridanus, and the beautiful bluish-white 
double star, Alpha Crucis, the brightest of the four 
stars that form the Southern Cross. 

The constellation of the Southern Cross is the 
most noted of all the southern constellations. It 
serves as a timepiece for the southern hemisphere, 
just as the Great Dipper does for northern lands. 
It stands in a nearly upright position when cul- 
minating or passing the meridian. 

Early Spanish conquerors of Mexico and South 
America regarded this cross as a token of heaven's 
approval of their attempt to plant the Christian 
faith in the wilds of the New World. Upon the 
first maps of the southern hemisphere South Amer- 
ica appeared as "Terre Sancte Crucis/' the Land 
of the Holy Cross. 

The southern constellations Argo Navis, Crux 
331 



SPLENDORS OF THE SKY 



and Centaurus, are all traversed by the Milky 
Way. 

The galaxy in Argo Navis is crossed by many 
dark bars, and near the Southern Cross is the pe- 
culiar pear-shaped hole known as the Coal Sack. 
One of the most peculiar stars in the heavens is 
situated in southern skies and is invisible in our 
latitudes. This is Eta Argus, which lies in the 
midst of a nebula and possesses most unusual and 
irregular fluctuations of light which distinguish it 
from various classes of variable stars or temporary 
stars. 

As far back as the year 1677 this star was ob- 
served to fluctuate in brightness. Between that 
date and 1800 records show a great range of bright- 
ness. In 1843 it became brighter than any other 
star except Sirius. At present it is barely visible 
to the naked eye. When at its brightest, in 1843, 
it gave 25,000 times the amount of light that it 
does now. 

Far to the south in the circumpolar constellation 
Tucana is to be found the finest of all globular star 
clusters and in Argo Navis there is the finest ir- 
regular star cluster in the heavens. Two splendid 
globular star clusters, located in this large and 
332 



SPLENDORS OF THE SKY 



noted constellation, are visible even to the naked 
eye. In Argo we also find the largest and brightest 
of the naked eye nebulae. 

Of unusual interest in the southern hemisphere 
are the Lesser and Greater Magellanic Clouds. 
They look very much like small star clouds de- 
tached from the girdle of the galaxy which en- 
circles the heavens. 

The Magellanic Clouds are rich in nebulae, va- 
riable stars and star clusters and the Greater Cloud 
has a decidedly spiral form. It has been suggested 
that our own stellar system, with its millions of 
stars, its galactic star clouds, its nebulae, variable 
stars and star clusters would present very much 
the same appearance that the Greater Magellanic 
Cloud does to us if it were transported to a dis- 
tance of a hundred thousand light years. 

Those who travel to the southern hemisphere are 
impressed by the fact that no bright star marks 
the south pole of the heavens. To locate the north 
pole we have the bright second magnitude star, 
Polaris, at the end of the handle of the Little Dip- 
per, and the two stars that outline the front of the 
bowl of the Big Dipper act as pointers to the pole 
star. 

333 



SPLENDORS OF THE SKY 



The seven stars of the Big Dipper are familiar 
to nearly every one in northern latitudes. As we 
pass southward the pole star sinks lower and lower 
toward the northern horizon, for its altitude above 
the horizon always equals the latitude of the ob- 
server. At the equator the north pole lies in the 
horizon, as does also the south pole. The belt of 
Orion crosses the meridian in the zenith. The view 
of the heavens from the tropics is probably unsur- 
passed, for we see from here the finest constella- 
tions of both hemispheres. 

As we pass into the Southern Hemisphere the 
Big Dipper gradually sinks below the northern 
horizon and we turn our eyes toward the unfamiliar 
constellations surrounding the south pole, which 
rises higher and higher in the sky as we go south- 
ward. Canopus in Argo Navis, brilliant Achernar 
and the four stars of the Southern Cross now 
mount high into the heavens and the dearth of 
bright stars in the neighborhood of the south pole 
is very evident. 

"We miss the familiar Dippers of northern lands 

encircling the north pole of the heavens and find it 

hard to accustom ourselves to circumpolar regions 

so different. Toward the northern horizon we now 

334 



SPLENDORS OF THE SKY 



see the familiar star groups that passed through 
our zenith in middle northern latitudes, the North- 
ern Cross, Lyra, and the Northern Crown, Bootes, 
Hercules, Perseus Andromeda and Pegasus usher-, 
ing in the different seasons. 



335 



CHAPTER XLIV 

THE ONE-HUNDRED INCH TELESCOPE OF THE MT. 
WILSON OBSERVATORY 

>Tp HE 100-inch mirror for the greatest reflecting 
■■- telescope in the world arrived safely at the 
summit of Mount Wilson, Cal., 5,700 feet above 
sea level, in July, 1917. 

The new reflector has a light gathering power 
three times as great as that of the five-foot reflector 
of the Mt. Wilson Observatory, which shows stars 
as faint as the twentieth magnitude. It will, there- 
fore, show stars one magnitude fainter. 

It is estimated that fully one hundred million 
additional faint stars are within reach of this great 
reflector. Some of these stars may be comparatively 
near to us, their feeble luminosity being due to the 
fact that they are dwarf suns ; others may be faint 
only because they lie on the outskirts of the uni- 
336 



SPLENDORS OF THE SKY 



verse. In actual luminosity such, stars would equal 
or surpass our own sun. 

Next to the 100-inch reflector in size comes the 
72-inch reflector of the Dominion Astrophysical 
Observatory which started on its observing career 
in the spring of 1918. The greatest refractor is 
the 40-inch telescope of the Yerkes Observatory. 
Reflecting and refracting telescopes differ radically 
in their treatment of the light received from the 
stars. In a refractor the rays of light pass through 
the lens at the upper end of the telescope tube 
and travel down the tube, coming to a focus at a 
point within. They are then examined by the ob- 
server by means of the eye-piece at the lower end of 
the telescope tube. In the reflecting type of tele- 
scope the mirror is placed at the lower end of the 
tube and reflects the incident ray back through the 
tube to a secondary mirror placed so as to receive it 
before it reaches a focus and to reflect it in turn to 
the observer or photographic plate placed at one 
side. 

It is possible to make reflectors much larger 
than refractors, since it is not essential that 
the glass be absolutely pure. In a reflecting tele- 
scope the function of the mirror is merely to act 
337 



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as a support for a thin silver coating which is 
deposited upon its upper concaved surface. Twice 
a year this silver coating must be renewed. 
Arrangements have been made to have this quickly 
and easily done in case of the new reflector. The 
mirror will be removed by means of an electric 
elevator to the resilvering room in the same build- 
ing. Since light does not penetrate the mirror, but 
is reflected from its highly polished surface to a 
secondary mirror and thence to the photographic 
plate or eye of the observer, it is not necessary that 
the glass entering into its composition have the 
high degree of perfection essential to the lens of a 
refracting telescope. The reflector is unsurpassed 
for photographic or spectroscopic work inasmuch 
as the quality of the light received is unchanged. 
In a refracting telescope the rays are always to 
some extent broken by passage through the lens. 
Perfect achromatism is the strongest point in favor 
of the reflector. 

The field of good definition for the great reflector 
is small, however, only equalling in area one-half 
the disk of the moon. This is a restriction placed 
by the necessity for rapid photographic action. 

Work upon the great reflector began in 1906, 
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SPLENDORS OF THE SKY 



when the St. Gobain glass works in France under- 
took to manufacture a block of glass large enough 
and perfect enough for a telescope of this size. 
After many attempts covering an interval of three 
years a satisfactory piece of glass for the great 
mirror was finally obtained and delivered at the 
optical shops of the Mount Wilson Observatory in 
Pasadena, Cal., twelve miles from the summit of 
Mount Wilson. 

Here for seven years it was to undergo a long 
process of grinding, polishing and figuring. All 
of this work was done by Prof. George Ritchey, a 
member of the staff of the observatory. In its fin- 
ished condition the mirror weighs four and a half 
tons and is nearly thirteen inches in thickness. 
This thickness is essential to prevent the mirror 
bending of its own weight. It has been subjected 
to many tests, increasing in refinement as the work 
progressed, and is now considered to be practically 
perfect. 

On July 1, 1917, it was packed in an octagonal 
shaped box lined with paraffin to keep out the dust 
and taken up the narrow winding mountain road 
six miles in length on a truck geared to a maximum 
speed of two miles an hour. Another truck pre- 
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SPLENDORS OF THE SKY 



ceded it, also a gang of workmen with tools to re- 
pair any defect in the road. The great sections of 
the casting were made at the Fore River Shipyards 
at Quincy, Mass., and shipped around Cape Horn, 
because they were refused as shipments by rail- 
roads, being too wide for flat cars and too high 
for tunnels. All parts of the great instrument that 
were not of unusual size and that required careful 
workmanship were designed and made at the in- 
strument shops of the observatory in Pasadena. 

The instrument is housed in a steel building with 
a 100-foot dome weighing 500 tons that revolves 
easily and rapidly by means of electrical ap- 
pliances. The moving parts of the great reflector, 
which weigh about 100 tons, are also electrically 
controlled. Every detail upon which the success- 
ful operation of the huge instrument depends has 
been carefully worked out by opticians and instru- 
ment makers connected with the observatory. 

The problems that the new instrument will assist 
in solving will be chiefly of an astrophysical nature 
in keeping with the lines of research undertaken by 
this observatory, such as the form and extent of 
the universe, the nature of star clusters and neb- 
ulae, the origin and evolution of stars and their 
340 



SPLENDORS OF THE SKY 



physical properties, streaming tendencies and ve- 
locities. Most of all this work will be done by- 
means of photographic and spectroscopic attach- 
ments and not by direct observations. 

At the present time special attention is being 
given to the red stars as bearing upon the question 
of the scattering of light in space. It has been ob- 
served that among stars fainter than the eighteenth 
magnitude there are few, if any, whiter than our 
own sun, which is classed as a yellow star, although 
faint white stars are present in the star clouds of 
the Milky Way. 

This preponderance of red stars among the 
faint stars, which are on the whole the most dis- 
tant, has led to the belief that minute particles of 
matter, cosmic dust, may scatter the light of dis- 
tant stars and give them a red tinge, just as the 
rays of the setting sun have a reddish tinge due 
to their passage through the dense, low-lying strata 
of the atmosphere. It is known, on the other 
hand, that stars also acquire a reddish tinge with 
advancing age and a lower temperature, and also 
that as a star advances in age its velocity increases, 
and so the question arises whether these faint stars 
may not be reddish because they are advanced in 

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SPLENDORS OF THE SKY 



type, and distant, because they have travelled far. 
It is one of the questions that the new instrument is 
well qualified to attack, since it is particularly 
adapted to a study of faint, distant stars. 

It is also peculiarly fitted to investigate the mys- 
terious spiral nebulae, especially the smaller mem- 
bers of the class. Are they "island universes,' ' 
faint because of great distance, or do they repre- 
sent the first stages in the birth of star systems 
comparatively near and small? There are spirals 
of all degrees and magnitudes, from the Great 
Spiral in Andromeda, visible to the naked eye, to 
the faintest specks of spiral form visible in the 
large telescopes. What will the great reflectors 
have to tell of these wonderful formations? 

The feelings of the explorer must come to those 
first privileged to guide this mighty instrument 
and penetrate into regions of space hitherto unex- 
plored. Man stands upon his tiny planet, which 
is but an atom in the universe, and tries to extend 
his vision further and further into the eternity of 
life that flows in a ceaseless cycle of change before 
his eyes. Very slowly and laboriously and heavily 
handicapped he tries to solve, step by step, the 
mighty riddle of creation. 
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SPLENDORS OF THE SKY 



One more step forward will be taken when this 
noble instrument is turned toward the heavens and 
those who have labored long and tirelessly to make 
it worthy of its task begin to gather the precious 
fruits of their labors. 



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